10 métodos de array JavaScript obrigatórios

Vamos ver quais filtros, forEach, some, every, includes, map, reduce, sort, find e findIndex são e como você pode usá-los.

ÍNDICE

• 1. filter()
• 2. forEach()
• 3. some()
• 4. every()
• 5. includes()
• 6. map()
• 7. reduce()
• 8. sort()
• 9. find()
• 10. findIndex()

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1. filter()

filteré o método sempre que você quiser, bem, filtrar valores. Quer apenas valores positivos? Apenas procurando por objetos que possuem uma determinada propriedade? filteré o seu caminho.

Segue a assinatura do filtermétodo:

filter(function (element, index, array) {
  // element is the element within the array
  // index is the index of the element in the array
  // array is a reference to the array filter works on
}, thisOverride);
// thisOverride is a way to override the semantical this within the callback function.
// If you set it to another object, calling this.anyThing would access anyThing within that
// object, and not the actual array.

Caso de uso de exemplo

Imagine que você tem uma loja online. E agora você deseja enviar um código de desconto para todos os clientes que moram em uma determinada área.

const getElibigleCustomers(customers, zipCode) {
  return customers.filter(
    (customer) => customer.address.zipCode === zipCode
  );
}

getElibigleCustomersretorna todos os clientes que possuem um endereço armazenado com um CEP, que é o mesmo CEP que você procura. Todos os outros clientes são filtrados da matriz.

Reimplementando filtro

Se você quiser entender filterainda melhor, vamos tentar reimplementá-lo.

function filter(callbackFn) {
  const newArray = [];

  for (let i = 0; i < this.length; i++) {
    if (callbackFn(this[i], i, this)) {
      newArray.push(this[i]);
    }
  }

  return newArray;
}

Array.prototype.filter = filter;

Atenção: Tenha em mente que você nunca deve substituir um método de protótipo de um tipo embutido. Mas isso é apenas para mostrar como uma possível implementação pode parecer.

Como você vê, filternada mais é do que um loop que executa uma função de retorno de chamada para cada elemento. Todos os elementos para os quais a função de retorno de chamada retorna false são filtrados.

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2. forEach()

forEaché uma maneira funcional de fazer um loop sobre os elementos da matriz e executar alguma lógica para cada elemento. O método em si não retorna um novo array.

Segue a assinatura do forEachmétodo:

forEach(function (element, index, array) {
  // element is the element within the array
  // index is the index of the element in the array
  // array is a reference to the array forEach works on
}, thisOverride);
// thisOverride is a way to override the semantical this within the callback function.
// If you set it to another object, calling this.anyThing would access anyThing within that
// object, and not the actual array.

Caso de uso de exemplo

Fiquemos com o exemplo da loja online. Agora, você deseja imprimir todos os nomes dos clientes filtrados anteriormente.

getElibigleCustomers(customers, '123456')
  .forEach(
    (customer) => console.log(`${customer.forename} ${customer.surname}`)
  );

Quando forEach é executado, o console imprime o nome completo de todos os clientes que foram filtrados anteriormente.

Reimplementando forEach

Vamos reimplementar forEachpara você entender melhor como funciona.

function forEach(callbackFn) {
  for (let i = 0; i < this.length; i++) {
    callbackFn(this[i], i, this);
  }
}

Array.prototype.forEach = forEach;

Mais uma vez, tenha em mente que você nunca deve substituir métodos de protótipo de tipos internos em um aplicativo real, exceto que você realmente sabe o que está fazendo.

Você provavelmente começa a notar um padrão agora. forEaché, mais uma vez, nada mais do que um loop. E dentro desse loop, a função de retorno de chamada é chamada. O resultado não é interessante e, portanto, jogado fora.

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3. some()

someé um método de matriz especial. Ele testa se pelo menos um elemento dentro da matriz é positivo para uma condição específica. Se sim, someretorna verdadeiro, caso contrário, retorna falso.

Segue a assinatura do somemétodo:

some(function (element, index, array) {
  // element is the element within the array
  // index is the index of the element in the array
  // array is a reference to the array some works on
}, thisOverride);
// thisOverride is a way to override the semantical this within the callback function.
// If you set it to another object, calling this.anyThing would access anyThing within that
// object, and not the actual array.

Caso de uso de exemplo

De volta ao nosso exemplo de loja online. Imagine que agora você deseja testar se pelo menos alguns dos clientes filtrados são menores de idade. Se sim, você quer mostrar a eles outro negócio, porque todos os outros recebem um desconto para bebidas alcoólicas. Mas você não quer apoiar crianças menores de idade bebendo, é claro.

const eligibleCustomers = getElibigleCustomers(customers, '123456')

const containsUnderAgedCustomers = eligibleCustomers.some(
  (customer) => customer.age < 18
);

Quando someexecutado, verifica a propriedade de idade de cada cliente. Se pelo menos um estiver abaixo de 18, retorna falso.

Reimplementando alguns

Hora de reimplementar some.

function some(callbackFn) {
  for (let i = 0; i < this.length; i++) {
    if (callbackFn(this[i], i, this)) {
      return true;
    }
  }
  return false;
}

Array.prototype.some = some;

somepercorre todos os elementos da matriz até encontrar um elemento em que a função de retorno de chamada retorne true para. Nesse caso, o método retorna mais cedo, pois para alguns elementos satisfazerem uma condição, uma já é suficiente. Somente quando nenhum elemento corresponde, false é retornado.

---

4. every()

everyé a contrapartida de some. Ele testa se todos os elementos satisfazem uma condição. Só então, o método retorna true. Se apenas um elemento falhar no teste, false será retornado.

Segue a assinatura do everymétodo:

every(function (element, index, array) {
  // element is the element within the array
  // index is the index of the element in the array
  // array is a reference to the array every works on
}, thisOverride);
// thisOverride is a way to override the semantical this within the callback function.
// If you set it to another object, calling this.anyThing would access anyThing within that
// object, and not the actual array.

Caso de uso de exemplo

Muitos clientes que receberam seu código de desconto já fizeram o pedido. Para economizar nos custos de envio, você deseja enviar tudo de uma vez. Mas primeiro, você precisa verificar se todos esses clientes têm dados de endereço válidos salvos.

const customersWhoOrdered = getCustomersForOrder('discount1234');

const allCustomersHaveValidShipmentData = customersWhoOrdered
  .every(
    (customer) => hasValidShipmentData(customer)
  );

Quando everyexecutado, ele passa cada cliente para uma função que verifica se esse cliente possui dados de remessa válidos armazenados. Se apenas um cliente tiver dados inválidos, toda a função retornará false.

Reimplementando cada

Hora de reimplementar every.

function every(callbackFn) {
  for (let i = 0; i < this.length; i++) {
    if (!callbackFn(this[i], i, this)) {
      return false;
    }
  }
  return true;
}

Array.prototype.every = every;

everypercorre todos os elementos da matriz até encontrar um elemento em que a função de retorno de chamada retorne false para. Nesse caso, o método retorna mais cedo, pois nem todos os elementos satisfazem a condição. Um já é suficiente. Somente quando nenhum elemento corresponde, true é retornado.

Você pode até ter notado que everynão é muito diferente de some. Em alguns pontos específicos, true é substituído por false e a verificação com a função de retorno de chamada é negada. Essas pequenas mudanças já são suficientes para que o método faça exatamente o que você deseja.

5. includes()

includesé um método que verifica se um array contém um elemento específico. É bom para uma verificação rápida, mas também tem suas desvantagens, das quais falaremos em um minuto.

Segue a assinatura do includesmétodo:

includes(function (searchElement, fromIndex) {
  // searchElement is the element you look for
  // fromIndex is the index the search should start at
});

Caso de uso de exemplo

includesé especial. Na verdade, ele testa a igualdade estrita, o que significa: ele procura um valor estritamente igual ao elemento de pesquisa ou procura a referência exata de um objeto.

Digamos que você queira verificar se os pedidos dos clientes incluem um pedido muito específico, como este:

const allOrders = getAllOrders();

const containsSpecificOrder = allOrders.includes({
  customer: 'John Doe'
  zipCode: '54321'
});

Você provavelmente ficaria surpreso ao descobrir que include retorna false, mesmo que a matriz contenha um objeto com exatamente as mesmas propriedades. Isso ocorre porque ele procura igualdade estrita, e os objetos só são estritamente iguais se forem a mesma referência. JavaScript não conhece um método equals.

Isso reduz includesos casos de uso a valores primitivos. Se você, por exemplo, deseja verificar se uma matriz de números contém um número específico como este:

const numbers = [1, 2, 3, 4, 5];

const includesFive = numbers.includes(5);

Aqui está uma regra prática: Se você lida com uma matriz de valores primitivos, use includes. Se você lida com objetos, use someporque permite passar um retorno de chamada com o qual você pode testar a igualdade dos objetos.

A reimplementação inclui

Hora de reimplementar includes.

function includes(searchElement, fromIndex = 0) {
  if (fromIndex > this.length || fromIndex < 0) {
    return false;
  }

  for (let i = fromIndex; i < this.length; i++) {
    if (this[i] === searchElement) {
      return true;
    }
  }

  return false;
}

Array.prototype.includes = includes;

As instruções guard no início estão lá para tornar a execução do método um pouco mais segura. Um fromIndex negativo não faz sentido, assim como um índice maior que o índice máximo do array. O resto é apenas um loop testando cada elemento para igualdade estrita com o elemento procurado.

6. map()

mapé um dos métodos de array mais importantes que existem. Sempre que você quiser transformar todos os valores dentro de um array, mapé o caminho a seguir.

Segue a assinatura do mapmétodo:

map(function (element, index, array) {
  // element is the element within the array
  // index is the index of the element in the array
  // array is a reference to the array map works on
}, thisOverride);
// thisOverride is a way to override the semantical this within the callback function.
// If you set it to another object, calling this.anyThing would access anyThing within that
// object, and not the actual array.

Caso de uso de exemplo

Vamos voltar ao ponto em que todos os clientes qualificados foram filtrados. Agora, você deseja enviar seus pedidos e precisa obter todos os endereços. Este é um ótimo caso de uso para o mapa:

const eligibleCustomers = getElibigleCustomers(customers, '123456');

const addresses = eligibleCustomers
  .map((customer) => customer.address);

mapitera sobre todos os clientes e, em seguida, extrai todos os endereços. Estes são colocados em uma nova matriz e retornados da função.

Reimplementando mapa

Hora de reimplementar map.

function map(callbackFn) {
  const newArray = [];
  for (let i = 0; i < this.length; i++) {
    const mappedValue = callbackFn(this[i], i, this);
    newArray.push(mappedValue);
  }
  return newArray;
}

Array.prototype.map = map;

mapitera sobre todos os elementos da matriz. Para cada elemento, ele chama a função de retorno de chamada e espera que um novo valor seja retornado. Esse valor é então enviado para uma nova matriz. Essa matriz é retornada por completo, resultando em uma matriz do mesmo tamanho que a original, mas provavelmente com elementos diferentes.

7. reduce()

reduceé o método de array mais poderoso existente. Ele pode ser usado para reimplementar todos os métodos de array existentes e é o mais flexível. Falar sobre todas as vantagens que ele oferece definitivamente precisaria de um artigo próprio, mas você terá um vislumbre dele em breve.

Segue a assinatura do reducemétodo:

reduce(function (accumulator, currentValue, currentIndex, array) {
  // accumulator is the result of the last call, or the initialValue in the beginning
  // currentValue is the value currently processed
  // currentIndex is the index of the current value within the array
  // array is a reference to the array reduce works on
}, initialValue);

Caso de uso de exemplo

Lembra quando você queria descobrir se havia clientes menores de idade? Outra maneira de lidar com esse problema é agrupar todos os clientes qualificados em dois grupos. Os maiores de idade e os menores de idade.

const eligibleCustomers = getElibigleCustomers(customers, '123456');

const customerGroups = eligibleCustomers
  .reduce((accumulator, customer) => {
    if (customer.age > 18) {
      accumulator[0].push(customer);
    } else {
      accumulator[1].push(customer);
    }
    return accumulator;
  }, [[], []]);

reducepode ser bem difícil de entender, mas podemos examinar o código acima juntos e ver o que ele faz. Neste caso, o acumulador é um array bidimensional. O índice 0 contém todos os clientes >= 18 anos de idade. O índice 1 contém todos os clientes menores de idade. Na primeira vez que a redução é executada, ela define o acumulador para a matriz bidimensional vazia. Dentro do método, o código verifica se a propriedade age do cliente está acima de 18. Em caso afirmativo, ele envia o cliente para a primeira matriz. Se o cliente for menor de idade, ele será enviado para a segunda matriz. No final, o array bidimensional com os clientes agrupados é retornado.

Reimplementando reduzir

Hora de reimplementar reduce.

function reduce(callbackFn, initialValue) {
  let accumulator = initialValue ?? this[0];
  for (let i = 0; i < this.length; i++) {
    accumulator = callbackFn(accumulator, this[i], i, this);
  }
  return accumulator;
}

Array.prototype.reduce = reduce;

reduceitera sobre todos os elementos como todos os outros métodos de array fazem. No início, o método precisa decidir se um valorInicial foi fornecido. Caso contrário, o primeiro elemento da matriz é considerado como tal. Depois disso, o acumulador é substituído pelo resultado de chamar o retorno de chamada a cada vez e, em seguida, retornado em sua forma final no final.

8. sort()

O nome de sortjá diz tudo. Sempre que você quiser ordenar um array, este é o método que você precisa chamar.

Segue a assinatura do sortmétodo:

sort(function (firstElement, secondElement) {
  // firstElement is the first element to compare
  // secondElement is the second element to compare
});

Caso de uso de exemplo

Sempre que você precisa classificar algo, você encontrou um caso de uso para sort. Vamos, por exemplo, tentar classificar seus clientes por idade. Para tal caso, sortpermite passar uma função de comparação que você pode usar para dizer sortcomo ordená-los corretamente.

const customers = getCustomers();

customers.sort((a, b) => customer.a - customer.b);

A função de retorno de chamada deve retornar um número com base na ordem dos elementos. Deve retornar um valor < 0 se a vier antes de b, 0 se ambos forem iguais e um valor > 0 se a vier depois de b.

Reimplementando classificação

A reimplementação sorté um pouco difícil porque, sob o capô, os tempos de execução podem implementar qualquer algoritmo de classificação que pareçam adequados. Existem apenas alguns requisitos, como que o algoritmo deve ser estável. Normalmente, os tempos de execução implementam pelo menos QuickSort e, às vezes, alteram a implementação com base nos elementos da matriz.

function partition(array, left, right, compareFunction) {
  let pivot = array[Math.floor((right + left) / 2)];
  let i = left;
  let j = right;
    while (i <= j) {
        while (compareFunction(array[i], pivot) < 0) {
            i++;
        }
        while (compareFunction(array[j], pivot) > 0) {
            j--;
        }
        if (i <= j) {
            [array[i], array[j]] = [array[j], array[i]]
            i++;
            j--;
        }
    }
    return i;
}

function quickSort(array, left, right, compareFunction) {
  let index;
  if (array.length > 1) {
      index = partition(array, left, right, compareFunction);
      if (left < index - 1) {
          quickSort(array, left, index - 1, compareFunction);
      }
      if (index < right) {
          quickSort(array, index, right, compareFunction);
      }
  }
  return array;
}

function sort(compareFunction) {
  return quickSort(this, 0, this.length - 1, compareFunction);
}

Array.prototype.sort = sort;

Esta é apenas uma implementação exemplar de classificação, neste caso, QuickSort. Mas deve dar-lhe uma ideia geral.

9. find()

findé a sua função de pesquisa. Sempre que você procura algo dentro de um array, você pode usar findpara recuperar o primeiro elemento do array que satisfaça suas condições.

Segue a assinatura do findmétodo:

find(function (element, index, array) {
  // element is the current element
  // index is the current index
  // array is a reference to the array find works on
}, thisOverride);
// thisOverride is a way to override the semantical this within the callback function.
// If you set it to another object, calling this.anyThing would access anyThing within that
// object, and not the actual array.

Caso de uso de exemplo

Imagine que você tente encontrar um cliente com um nome específico em todos os seus clientes.

const customers = getCustomers();

const customerJohn = customers.find(
  (customer) => customer.forename === 'John'
);

Neste caso, findretorna o primeiro usuário dentro do array que tem o nome próprio John. O importante é que findnão retornará todos os clientes com esse nome.

Reimplementando encontrar

Hora de reimplementar find.

function find(callbackFn) {
  for (let i = 0; i < this.length; i++) {
    if (callbackFn(this[i], i, this)) {
      return this[i];
    }
  }
  return undefined;
}

Array.prototype.find = find;

finditera sobre todos os elementos como todos os outros métodos de array fazem. Para cada elemento, ele verifica se a função de retorno de chamada retorna true. Se isso acontecer, ele retornará o elemento nessa posição. Se não retornar mais cedo, retornará indefinido no final.

10. findIndex()

findIndexé um método que você pode usar para obter o índice de um elemento dentro da matriz. Como find, ele para no primeiro elemento que satisfaz a condição. Assim, ele retornará apenas o índice do primeiro elemento que satisfaça o teste.

Segue a assinatura do findIndexmétodo:

findIndex(function (element, index, array) {
  // element is the current element
  // index is the current index
  // array is a reference to the array find works on
}, thisOverride);
// thisOverride is a way to override the semantical this within the callback function.
// If you set it to another object, calling this.anyThing would access anyThing within that
// object, and not the actual array.

Caso de uso de exemplo

Imagine que você tenha todos os seus clientes classificados por idade e agora deseja encontrar o primeiro cliente com o nome próprio John.

const customers = getCustomers();
const customersSortedByAge = sortByAge(customers);

const indexOfJohn customersSortedByAge.findIndex((customer) => customer.forename === 'John');
const customerJohn = customersSortedByAge[indexOfJohn];

Neste caso findIndexretorna o índice do primeiro usuário dentro do array que tem o nome próprio John. O importante é que findIndexnão retornará todos os índices de clientes com esse nome.

Reimplementando findIndex

Hora de reimplementar findIndex.

function findIndex(callbackFn) {
  for (let i = 0; i < this.length; i++) {
    if (callbackFn(this[i], i, this)) {
      return i;
    }
  }
  return -1;
}

Array.prototype.findIndex = findIndex;

findIndexitera sobre todos os elementos como todos os outros métodos de array fazem. Você deve notar a semelhança com find. Em vez de retornar o elemento, somente o índice é retornado quando um elemento é encontrado. Em vez de indefinido, se nada for encontrado, -1 será retornado.

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How to Create Arrays in Python

In this tutorial, you'll know the basics of how to create arrays in Python using the array module. Learn how to use Python arrays. You'll see how to define them and the different methods commonly used for performing operations on them.

This tutorialvideo on 'Arrays in Python' will help you establish a strong hold on all the fundamentals in python programming language. Below are the topics covered in this video:  
1:15 What is an array?
2:53 Is python list same as an array?
3:48  How to create arrays in python?
7:19 Accessing array elements
9:59 Basic array operations
        - 10:33  Finding the length of an array
        - 11:44  Adding Elements
        - 15:06  Removing elements
        - 18:32  Array concatenation
       - 20:59  Slicing
       - 23:26  Looping  

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Python Array Tutorial – Define, Index, Methods

In this article, you'll learn how to use Python arrays. You'll see how to define them and the different methods commonly used for performing operations on them.

The artcile covers arrays that you create by importing the array module. We won't cover NumPy arrays here.

Table of Contents

1. Introduction to Arrays
   1. The differences between Lists and Arrays
   2. When to use arrays
2. How to use arrays
   1. Define arrays
   2. Find the length of arrays
   3. Array indexing
   4. Search through arrays
   5. Loop through arrays
   6. Slice an array
3. Array methods for performing operations
   1. Change an existing value
   2. Add a new value
   3. Remove a value
4. Conclusion

Let's get started!

What are Python Arrays?

Arrays are a fundamental data structure, and an important part of most programming languages. In Python, they are containers which are able to store more than one item at the same time.

Specifically, they are an ordered collection of elements with every value being of the same data type. That is the most important thing to remember about Python arrays - the fact that they can only hold a sequence of multiple items that are of the same type.

What's the Difference between Python Lists and Python Arrays?

Lists are one of the most common data structures in Python, and a core part of the language.

Lists and arrays behave similarly.

Just like arrays, lists are an ordered sequence of elements.

They are also mutable and not fixed in size, which means they can grow and shrink throughout the life of the program. Items can be added and removed, making them very flexible to work with.

However, lists and arrays are not the same thing.

Lists store items that are of various data types. This means that a list can contain integers, floating point numbers, strings, or any other Python data type, at the same time. That is not the case with arrays.

As mentioned in the section above, arrays store only items that are of the same single data type. There are arrays that contain only integers, or only floating point numbers, or only any other Python data type you want to use.

When to Use Python Arrays

Lists are built into the Python programming language, whereas arrays aren't. Arrays are not a built-in data structure, and therefore need to be imported via the array module in order to be used.

Arrays of the array module are a thin wrapper over C arrays, and are useful when you want to work with homogeneous data.

They are also more compact and take up less memory and space which makes them more size efficient compared to lists.

If you want to perform mathematical calculations, then you should use NumPy arrays by importing the NumPy package. Besides that, you should just use Python arrays when you really need to, as lists work in a similar way and are more flexible to work with.

How to Use Arrays in Python

In order to create Python arrays, you'll first have to import the array module which contains all the necassary functions.

There are three ways you can import the array module:

• By using import array at the top of the file. This includes the module array. You would then go on to create an array using array.array().

import array

#how you would create an array
array.array()

• Instead of having to type array.array() all the time, you could use import array as arr at the top of the file, instead of import array alone. You would then create an array by typing arr.array(). The arr acts as an alias name, with the array constructor then immediately following it.

import array as arr

#how you would create an array
arr.array()

• Lastly, you could also use from array import *, with * importing all the functionalities available. You would then create an array by writing the array() constructor alone.

from array import *

#how you would create an array
array()

How to Define Arrays in Python

Once you've imported the array module, you can then go on to define a Python array.

The general syntax for creating an array looks like this:

variable_name = array(typecode,[elements])

Let's break it down:

• variable_name would be the name of the array.
• The typecode specifies what kind of elements would be stored in the array. Whether it would be an array of integers, an array of floats or an array of any other Python data type. Remember that all elements should be of the same data type.
• Inside square brackets you mention the elements that would be stored in the array, with each element being separated by a comma. You can also create an empty array by just writing variable_name = array(typecode) alone, without any elements.

Below is a typecode table, with the different typecodes that can be used with the different data types when defining Python arrays:

TYPECODE	C TYPE	PYTHON TYPE	SIZE
'b'	signed char	int	1
'B'	unsigned char	int	1
'u'	wchar_t	Unicode character	2
'h'	signed short	int	2
'H'	unsigned short	int	2
'i'	signed int	int	2
'I'	unsigned int	int	2
'l'	signed long	int	4
'L'	unsigned long	int	4
'q'	signed long long	int	8
'Q'	unsigned long long	int	8
'f'	float	float	4
'd'	double	float	8

Tying everything together, here is an example of how you would define an array in Python:

import array as arr 

numbers = arr.array('i',[10,20,30])


print(numbers)

#output

#array('i', [10, 20, 30])

Let's break it down:

• First we included the array module, in this case with import array as arr .
• Then, we created a numbers array.
• We used arr.array() because of import array as arr .
• Inside the array() constructor, we first included i, for signed integer. Signed integer means that the array can include positive and negative values. Unsigned integer, with H for example, would mean that no negative values are allowed.
• Lastly, we included the values to be stored in the array in square brackets.

Keep in mind that if you tried to include values that were not of i typecode, meaning they were not integer values, you would get an error:

import array as arr 

numbers = arr.array('i',[10.0,20,30])


print(numbers)

#output

#Traceback (most recent call last):
# File "/Users/dionysialemonaki/python_articles/demo.py", line 14, in <module>
#   numbers = arr.array('i',[10.0,20,30])
#TypeError: 'float' object cannot be interpreted as an integer

In the example above, I tried to include a floating point number in the array. I got an error because this is meant to be an integer array only.

Another way to create an array is the following:

from array import *

#an array of floating point values
numbers = array('d',[10.0,20.0,30.0])

print(numbers)

#output

#array('d', [10.0, 20.0, 30.0])

The example above imported the array module via from array import * and created an array numbers of float data type. This means that it holds only floating point numbers, which is specified with the 'd' typecode.

How to Find the Length of an Array in Python

To find out the exact number of elements contained in an array, use the built-in len() method.

It will return the integer number that is equal to the total number of elements in the array you specify.

import array as arr 

numbers = arr.array('i',[10,20,30])


print(len(numbers))

#output
# 3

In the example above, the array contained three elements – 10, 20, 30 – so the length of numbers is 3.

Array Indexing and How to Access Individual Items in an Array in Python

Each item in an array has a specific address. Individual items are accessed by referencing their index number.

Indexing in Python, and in all programming languages and computing in general, starts at 0. It is important to remember that counting starts at 0 and not at 1.

To access an element, you first write the name of the array followed by square brackets. Inside the square brackets you include the item's index number.

The general syntax would look something like this:

array_name[index_value_of_item]

Here is how you would access each individual element in an array:

import array as arr 

numbers = arr.array('i',[10,20,30])

print(numbers[0]) # gets the 1st element
print(numbers[1]) # gets the 2nd element
print(numbers[2]) # gets the 3rd element

#output

#10
#20
#30

Remember that the index value of the last element of an array is always one less than the length of the array. Where n is the length of the array, n - 1 will be the index value of the last item.

Note that you can also access each individual element using negative indexing.

With negative indexing, the last element would have an index of -1, the second to last element would have an index of -2, and so on.

Here is how you would get each item in an array using that method:

import array as arr 

numbers = arr.array('i',[10,20,30])

print(numbers[-1]) #gets last item
print(numbers[-2]) #gets second to last item
print(numbers[-3]) #gets first item
 
#output

#30
#20
#10

How to Search Through an Array in Python

You can find out an element's index number by using the index() method.

You pass the value of the element being searched as the argument to the method, and the element's index number is returned.

import array as arr 

numbers = arr.array('i',[10,20,30])

#search for the index of the value 10
print(numbers.index(10))

#output

#0

If there is more than one element with the same value, the index of the first instance of the value will be returned:

import array as arr 


numbers = arr.array('i',[10,20,30,10,20,30])

#search for the index of the value 10
#will return the index number of the first instance of the value 10
print(numbers.index(10))

#output

#0

How to Loop through an Array in Python

You've seen how to access each individual element in an array and print it out on its own.

You've also seen how to print the array, using the print() method. That method gives the following result:

import array as arr 

numbers = arr.array('i',[10,20,30])

print(numbers)

#output

#array('i', [10, 20, 30])

What if you want to print each value one by one?

This is where a loop comes in handy. You can loop through the array and print out each value, one-by-one, with each loop iteration.

For this you can use a simple for loop:

import array as arr 

numbers = arr.array('i',[10,20,30])

for number in numbers:
    print(number)
    
#output
#10
#20
#30

You could also use the range() function, and pass the len() method as its parameter. This would give the same result as above:

import array as arr  

values = arr.array('i',[10,20,30])

#prints each individual value in the array
for value in range(len(values)):
    print(values[value])

#output

#10
#20
#30

How to Slice an Array in Python

To access a specific range of values inside the array, use the slicing operator, which is a colon :.

When using the slicing operator and you only include one value, the counting starts from 0 by default. It gets the first item, and goes up to but not including the index number you specify.

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#get the values 10 and 20 only
print(numbers[:2])  #first to second position

#output

#array('i', [10, 20])

When you pass two numbers as arguments, you specify a range of numbers. In this case, the counting starts at the position of the first number in the range, and up to but not including the second one:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])


#get the values 20 and 30 only
print(numbers[1:3]) #second to third position

#output

#rray('i', [20, 30])

Methods For Performing Operations on Arrays in Python

Arrays are mutable, which means they are changeable. You can change the value of the different items, add new ones, or remove any you don't want in your program anymore.

Let's see some of the most commonly used methods which are used for performing operations on arrays.

How to Change the Value of an Item in an Array

You can change the value of a specific element by speficying its position and assigning it a new value:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#change the first element
#change it from having a value of 10 to having a value of 40
numbers[0] = 40

print(numbers)

#output

#array('i', [40, 20, 30])

How to Add a New Value to an Array

To add one single value at the end of an array, use the append() method:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#add the integer 40 to the end of numbers
numbers.append(40)

print(numbers)

#output

#array('i', [10, 20, 30, 40])

Be aware that the new item you add needs to be the same data type as the rest of the items in the array.

Look what happens when I try to add a float to an array of integers:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#add the integer 40 to the end of numbers
numbers.append(40.0)

print(numbers)

#output

#Traceback (most recent call last):
#  File "/Users/dionysialemonaki/python_articles/demo.py", line 19, in <module>
#   numbers.append(40.0)
#TypeError: 'float' object cannot be interpreted as an integer

But what if you want to add more than one value to the end an array?

Use the extend() method, which takes an iterable (such as a list of items) as an argument. Again, make sure that the new items are all the same data type.

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#add the integers 40,50,60 to the end of numbers
#The numbers need to be enclosed in square brackets

numbers.extend([40,50,60])

print(numbers)

#output

#array('i', [10, 20, 30, 40, 50, 60])

And what if you don't want to add an item to the end of an array? Use the insert() method, to add an item at a specific position.

The insert() function takes two arguments: the index number of the position the new element will be inserted, and the value of the new element.

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#add the integer 40 in the first position
#remember indexing starts at 0

numbers.insert(0,40)

print(numbers)

#output

#array('i', [40, 10, 20, 30])

How to Remove a Value from an Array

To remove an element from an array, use the remove() method and include the value as an argument to the method.

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

numbers.remove(10)

print(numbers)

#output

#array('i', [20, 30])

With remove(), only the first instance of the value you pass as an argument will be removed.

See what happens when there are more than one identical values:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30,10,20])

numbers.remove(10)

print(numbers)

#output

#array('i', [20, 30, 10, 20])

Only the first occurence of 10 is removed.

You can also use the pop() method, and specify the position of the element to be removed:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30,10,20])

#remove the first instance of 10
numbers.pop(0)

print(numbers)

#output

#array('i', [20, 30, 10, 20])

Conclusion

And there you have it - you now know the basics of how to create arrays in Python using the array module. Hopefully you found this guide helpful.

Thanks for reading and happy coding!

#python #programming 

Understanding Arrays in Python

Learn how to use Python arrays. Create arrays in Python using the array module. You'll see how to define them and the different methods commonly used for performing operations on them.
 

The artcile covers arrays that you create by importing the array module. We won't cover NumPy arrays here.

Table of Contents

1. Introduction to Arrays
   1. The differences between Lists and Arrays
   2. When to use arrays
2. How to use arrays
   1. Define arrays
   2. Find the length of arrays
   3. Array indexing
   4. Search through arrays
   5. Loop through arrays
   6. Slice an array
3. Array methods for performing operations
   1. Change an existing value
   2. Add a new value
   3. Remove a value
4. Conclusion

Let's get started!

---

What are Python Arrays?

Arrays are a fundamental data structure, and an important part of most programming languages. In Python, they are containers which are able to store more than one item at the same time.

Specifically, they are an ordered collection of elements with every value being of the same data type. That is the most important thing to remember about Python arrays - the fact that they can only hold a sequence of multiple items that are of the same type.

What's the Difference between Python Lists and Python Arrays?

Lists are one of the most common data structures in Python, and a core part of the language.

Lists and arrays behave similarly.

Just like arrays, lists are an ordered sequence of elements.

They are also mutable and not fixed in size, which means they can grow and shrink throughout the life of the program. Items can be added and removed, making them very flexible to work with.

However, lists and arrays are not the same thing.

Lists store items that are of various data types. This means that a list can contain integers, floating point numbers, strings, or any other Python data type, at the same time. That is not the case with arrays.

As mentioned in the section above, arrays store only items that are of the same single data type. There are arrays that contain only integers, or only floating point numbers, or only any other Python data type you want to use.

When to Use Python Arrays

Lists are built into the Python programming language, whereas arrays aren't. Arrays are not a built-in data structure, and therefore need to be imported via the array module in order to be used.

Arrays of the array module are a thin wrapper over C arrays, and are useful when you want to work with homogeneous data.

They are also more compact and take up less memory and space which makes them more size efficient compared to lists.

If you want to perform mathematical calculations, then you should use NumPy arrays by importing the NumPy package. Besides that, you should just use Python arrays when you really need to, as lists work in a similar way and are more flexible to work with.

How to Use Arrays in Python

In order to create Python arrays, you'll first have to import the array module which contains all the necassary functions.

There are three ways you can import the array module:

1. By using import array at the top of the file. This includes the module array. You would then go on to create an array using array.array().

import array

#how you would create an array
array.array()

1. Instead of having to type array.array() all the time, you could use import array as arr at the top of the file, instead of import array alone. You would then create an array by typing arr.array(). The arr acts as an alias name, with the array constructor then immediately following it.

import array as arr

#how you would create an array
arr.array()

1. Lastly, you could also use from array import *, with * importing all the functionalities available. You would then create an array by writing the array() constructor alone.

from array import *

#how you would create an array
array()

How to Define Arrays in Python

Once you've imported the array module, you can then go on to define a Python array.

The general syntax for creating an array looks like this:

variable_name = array(typecode,[elements])

Let's break it down:

• variable_name would be the name of the array.
• The typecode specifies what kind of elements would be stored in the array. Whether it would be an array of integers, an array of floats or an array of any other Python data type. Remember that all elements should be of the same data type.
• Inside square brackets you mention the elements that would be stored in the array, with each element being separated by a comma. You can also create an empty array by just writing variable_name = array(typecode) alone, without any elements.

Below is a typecode table, with the different typecodes that can be used with the different data types when defining Python arrays:

TYPECODE	C TYPE	PYTHON TYPE	SIZE
'b'	signed char	int	1
'B'	unsigned char	int	1
'u'	wchar_t	Unicode character	2
'h'	signed short	int	2
'H'	unsigned short	int	2
'i'	signed int	int	2
'I'	unsigned int	int	2
'l'	signed long	int	4
'L'	unsigned long	int	4
'q'	signed long long	int	8
'Q'	unsigned long long	int	8
'f'	float	float	4
'd'	double	float	8

Tying everything together, here is an example of how you would define an array in Python:

import array as arr 

numbers = arr.array('i',[10,20,30])


print(numbers)

#output

#array('i', [10, 20, 30])

Let's break it down:

• First we included the array module, in this case with import array as arr .
• Then, we created a numbers array.
• We used arr.array() because of import array as arr .
• Inside the array() constructor, we first included i, for signed integer. Signed integer means that the array can include positive and negative values. Unsigned integer, with H for example, would mean that no negative values are allowed.
• Lastly, we included the values to be stored in the array in square brackets.

Keep in mind that if you tried to include values that were not of i typecode, meaning they were not integer values, you would get an error:

import array as arr 

numbers = arr.array('i',[10.0,20,30])


print(numbers)

#output

#Traceback (most recent call last):
# File "/Users/dionysialemonaki/python_articles/demo.py", line 14, in <module>
#   numbers = arr.array('i',[10.0,20,30])
#TypeError: 'float' object cannot be interpreted as an integer

In the example above, I tried to include a floating point number in the array. I got an error because this is meant to be an integer array only.

Another way to create an array is the following:

from array import *

#an array of floating point values
numbers = array('d',[10.0,20.0,30.0])

print(numbers)

#output

#array('d', [10.0, 20.0, 30.0])

The example above imported the array module via from array import * and created an array numbers of float data type. This means that it holds only floating point numbers, which is specified with the 'd' typecode.

How to Find the Length of an Array in Python

To find out the exact number of elements contained in an array, use the built-in len() method.

It will return the integer number that is equal to the total number of elements in the array you specify.

import array as arr 

numbers = arr.array('i',[10,20,30])


print(len(numbers))

#output
# 3

In the example above, the array contained three elements – 10, 20, 30 – so the length of numbers is 3.

Array Indexing and How to Access Individual Items in an Array in Python

Each item in an array has a specific address. Individual items are accessed by referencing their index number.

Indexing in Python, and in all programming languages and computing in general, starts at 0. It is important to remember that counting starts at 0 and not at 1.

To access an element, you first write the name of the array followed by square brackets. Inside the square brackets you include the item's index number.

The general syntax would look something like this:

array_name[index_value_of_item]

Here is how you would access each individual element in an array:

import array as arr 

numbers = arr.array('i',[10,20,30])

print(numbers[0]) # gets the 1st element
print(numbers[1]) # gets the 2nd element
print(numbers[2]) # gets the 3rd element

#output

#10
#20
#30

Remember that the index value of the last element of an array is always one less than the length of the array. Where n is the length of the array, n - 1 will be the index value of the last item.

Note that you can also access each individual element using negative indexing.

With negative indexing, the last element would have an index of -1, the second to last element would have an index of -2, and so on.

Here is how you would get each item in an array using that method:

import array as arr 

numbers = arr.array('i',[10,20,30])

print(numbers[-1]) #gets last item
print(numbers[-2]) #gets second to last item
print(numbers[-3]) #gets first item
 
#output

#30
#20
#10

How to Search Through an Array in Python

You can find out an element's index number by using the index() method.

You pass the value of the element being searched as the argument to the method, and the element's index number is returned.

import array as arr 

numbers = arr.array('i',[10,20,30])

#search for the index of the value 10
print(numbers.index(10))

#output

#0

If there is more than one element with the same value, the index of the first instance of the value will be returned:

import array as arr 


numbers = arr.array('i',[10,20,30,10,20,30])

#search for the index of the value 10
#will return the index number of the first instance of the value 10
print(numbers.index(10))

#output

#0

How to Loop through an Array in Python

You've seen how to access each individual element in an array and print it out on its own.

You've also seen how to print the array, using the print() method. That method gives the following result:

import array as arr 

numbers = arr.array('i',[10,20,30])

print(numbers)

#output

#array('i', [10, 20, 30])

What if you want to print each value one by one?

This is where a loop comes in handy. You can loop through the array and print out each value, one-by-one, with each loop iteration.

For this you can use a simple for loop:

import array as arr 

numbers = arr.array('i',[10,20,30])

for number in numbers:
    print(number)
    
#output
#10
#20
#30

You could also use the range() function, and pass the len() method as its parameter. This would give the same result as above:

import array as arr  

values = arr.array('i',[10,20,30])

#prints each individual value in the array
for value in range(len(values)):
    print(values[value])

#output

#10
#20
#30

How to Slice an Array in Python

To access a specific range of values inside the array, use the slicing operator, which is a colon :.

When using the slicing operator and you only include one value, the counting starts from 0 by default. It gets the first item, and goes up to but not including the index number you specify.

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#get the values 10 and 20 only
print(numbers[:2])  #first to second position

#output

#array('i', [10, 20])

When you pass two numbers as arguments, you specify a range of numbers. In this case, the counting starts at the position of the first number in the range, and up to but not including the second one:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])


#get the values 20 and 30 only
print(numbers[1:3]) #second to third position

#output

#rray('i', [20, 30])

Methods For Performing Operations on Arrays in Python

Arrays are mutable, which means they are changeable. You can change the value of the different items, add new ones, or remove any you don't want in your program anymore.

Let's see some of the most commonly used methods which are used for performing operations on arrays.

How to Change the Value of an Item in an Array

You can change the value of a specific element by speficying its position and assigning it a new value:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#change the first element
#change it from having a value of 10 to having a value of 40
numbers[0] = 40

print(numbers)

#output

#array('i', [40, 20, 30])

How to Add a New Value to an Array

To add one single value at the end of an array, use the append() method:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#add the integer 40 to the end of numbers
numbers.append(40)

print(numbers)

#output

#array('i', [10, 20, 30, 40])

Be aware that the new item you add needs to be the same data type as the rest of the items in the array.

Look what happens when I try to add a float to an array of integers:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#add the integer 40 to the end of numbers
numbers.append(40.0)

print(numbers)

#output

#Traceback (most recent call last):
#  File "/Users/dionysialemonaki/python_articles/demo.py", line 19, in <module>
#   numbers.append(40.0)
#TypeError: 'float' object cannot be interpreted as an integer

But what if you want to add more than one value to the end an array?

Use the extend() method, which takes an iterable (such as a list of items) as an argument. Again, make sure that the new items are all the same data type.

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#add the integers 40,50,60 to the end of numbers
#The numbers need to be enclosed in square brackets

numbers.extend([40,50,60])

print(numbers)

#output

#array('i', [10, 20, 30, 40, 50, 60])

And what if you don't want to add an item to the end of an array? Use the insert() method, to add an item at a specific position.

The insert() function takes two arguments: the index number of the position the new element will be inserted, and the value of the new element.

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#add the integer 40 in the first position
#remember indexing starts at 0

numbers.insert(0,40)

print(numbers)

#output

#array('i', [40, 10, 20, 30])

How to Remove a Value from an Array

To remove an element from an array, use the remove() method and include the value as an argument to the method.

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

numbers.remove(10)

print(numbers)

#output

#array('i', [20, 30])

With remove(), only the first instance of the value you pass as an argument will be removed.

See what happens when there are more than one identical values:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30,10,20])

numbers.remove(10)

print(numbers)

#output

#array('i', [20, 30, 10, 20])

Only the first occurence of 10 is removed.

You can also use the pop() method, and specify the position of the element to be removed:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30,10,20])

#remove the first instance of 10
numbers.pop(0)

print(numbers)

#output

#array('i', [20, 30, 10, 20])

Conclusion

And there you have it - you now know the basics of how to create arrays in Python using the array module. Hopefully you found this guide helpful.

You'll start from the basics and learn in an interacitve and beginner-friendly way. You'll also build five projects at the end to put into practice and help reinforce what you learned.

Thanks for reading and happy coding!

Original article source at https://www.freecodecamp.org

#python 

JavaScript Arrays Tutorial. DO NOT MISS!!!

Learn JavaScript Arrays

📺 The video in this post was made by Programming with Mosh
The origin of the article: https://www.youtube.com/watch?v=oigfaZ5ApsM&list=PLTjRvDozrdlxEIuOBZkMAK5uiqp8rHUax&index=4
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#arrays #javascript #javascript arrays #javascript arrays tutorial

Fill and Filter in Array in JavaScript

By the word Array methods, I mean the inbuilt array functions, which might be helpful for us in so many ways. So why not just explore and make use of them, to boost our productivity.

Let’s see them together one by one with some amazing examples.

Array.fill():

The _fill()_ method changes all elements in an array to a static value, from a start index (default _0_) to an end index (default _array.length_). It returns the modified array.

In simple words, it’s gonna fill the elements of the array with whatever sets of params, you pass in it. Mostly we pass three params, each param stands with some meaning. The first param value: what value you want to fill, second value: start range of index(inclusive), and third value: end range of index(exclusive). Imagine you are going to apply this method on some date, so that how its gonna look like eg: array.fill(‘Some date’, start date, end date).

NOTE: Start range is inclusive and end range is exclusive.

Let’s understand this in the below example-

//declare array
var testArray = [2,4,6,8,10,12,14];

console.log(testArray.fill("A"));

When you run this code, you gonna see all the elements of testArray will be replaced by 'A' like [“A”,"A","A","A","A","A","A"].

#javascript-tips #array-methods #javascript-development #javascript #arrays

A quick guide to JavaScript Arrays

Introduction

Arrays are a structure common to all programming languages so knowing what they are and having a firm grasp on what you’re able to accomplish with Arrays will take you a long way in your journey as a software developer. The code examples I share in this post will be in JavaScript but the concepts are common among all languages. What you learn here can easily be translated to any other language you work with.

In this post I’ll be covering how to perform the create, read update and delete operations using arrays, some common functions that come with the Array prototype and also how to implement them.

---

What is an Array

Before we jump into the juicy bits of Arrays, lets quickly gloss over what they are. Arrays

• are a fundamental data type in JavaScript
• are an ordered collection of values called **elements **that are stored at and accessed via an index
• are untyped, meaning that the elements of an array could be of different types. This allows us to create complex arrays such as an array of objects or even an array of arrays (multidimensional arrays)
• can have elements that are constants or expressions
• have a property called length that tells you the number of elements in the array
• inherit properties from Array.prototype that includes a wide variety useful functions that can be called from arrays or array-like objects

---

CRUD operations using Arrays

If you’re not familiar with the term CRUD it stands for Create, Read, Update and Delete. In this section we’ll go through each one of these operations and cover different ways you can perform each one.

Creating Arrays

There are several ways you can create an Array but the most common ways are by using

• the Array literal syntax
• the Array constructor i.e. new Array()

Lets take a look at each one with examples

Array literal

The array literal is the most common way of creating an array. It uses the square brackets as a notion of a container followed by comma separated values inside the square brackets. The following examples show how to use the array literal syntax and how arrays are untyped i.e. can contain elements of different types.

Examples of untyped arrays in JavaScript created with the array literal syntax.

Array constructor

Another way to create an array is through the Array constructor.

const myArray = new Array();

Using the Array constructor, as shown above, is the same as creating an array with the array literal syntax. i.e.

// The following two lines behave exactly the same way i.e. both create an empty arrays

const myArray = new Array();
const myOtherArray = [];

The array constructor, however, is able to receive arguments that allow it to behave in different ways depending on the number and type of arguments passed to it.

• You can pass a single numeric argument which creates an array of the specified length. This option is mostly used when you know how many elements you’ll be placing in the array

const myArray = new Array(5);

Note: If you want to define the array with a specified size, as shown above, the argument passed must be a numeric value. Any other type would be considered as the first element that’ll be placed in the array.

• Or you can pass two or more arguments or a non-numeric argument to place the values inside the array. This works the same way as shown in the array literal examples.

Examples of arrays created by using the Array constructor in JavaScript

As stated earlier, these two ways are the most common ways of creating arrays that you’ll see and use 99% of the time. There are a few other ways but we won’t dive deep into how they work. They are

• the spread operator const someArray = […someOtherArray]
• the static method Array.of()
• and the static method Array.from()

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