20 Fastest Methods to Easily identify Array's Operation in JavaScript

Methods to Get to Know JavaScript Array Operations

For example, Let’s create an Array.

var foods =  ["🍎", "🍊", "🍗", "🍕", "🥩"];

1. Filter

The filter() method creates a new array with elements that return true from the callback function.

var foods =  ["🍎", "🍊", "🍗", "🍕", "🥩"];

var vegFoods = foods.filter( (food) => isVeg(food) );

vegFoods; ["🍎", "🍊", "🍕"];

2. lastIndexOf

First last index of a given element in the Array, if it is not present, it returns -1.

var foods = ["🍎", "🍊", "🍗", "🍕", "🥩", "🍎"];

foods.lastIndexOf('🍎'); // 5

foods.lastIndexOf('🍔'); // -1

3. Length

Returns the number of an element of the Array.

foods.length; // 5

Tip: We can change the length property to delete elements.

foods.length = 0;

foods; // []

4. Push

Add an element to the end of an Array.

var foods =  ["🍎", "🍊", "🍗", "🍕", "🥩"];

foods.push('🍇');

foods; // ["🍎", "🍊", "🍗", "🍕", "🥩", "🍇"]

Tip: Use push with the spread operator (…) as an alternative to the concat method.

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

var num2 = [6,7,8,9,10];

numbers.push(...num2);

5. Unshift

Add an element to the beginning of an Array.

var foods =  ["🍎", "🍊", "🍗", "🍕", "🥩"];

foods.unshift('🍇');

foods; // ["🍇", "🍎", "🍊", "🍗", "🍕", "🥩"]

Tip: Use unshift with the spread operator (…) to concat elements at the beginning.

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

var num2 = [6,7,8,9,10];

numbers.unshift(...num2);

6. Pop

Removes the last element of the array.

var foods =  ["🍎", "🍊", "🍗", "🍕", "🥩"];

foods.pop();  // "🥩"

foods; // ["🍎", "🍊", "🍗", "🍕"]

Tip: We can use the pop method in stack implementation.

7. Shift

Remove the first element of the array.

var foods =  ["🍎", "🍊", "🍗", "🍕", "🥩"];

foods.shift();  // "🍎"

foods; // ["🍊", "🍗", "🍕", "🥩"]

Tip: We can use the shift method in dequeue operations on Queue implementation.

8. Join

Joins the elements of Array to String.

var foods =  ["🍎", "🍊", "🍗", "🍕", "🥩"];

var joinedFood = foods.join(); // "🍎,🍊,🍗,🍕,🥩";

var joinedFood1 = foods.join('--'); // "🍎--🍊--🍗--🍕--🥩"

Tip: Use as an alternative to string concatenation.

var arr = ['J','a','v', 'a'];

var str = '';

// without join

for(let i = 0, len = arr.length; i < len ; i++) {

     str += arr[i];
		 
}

// with join

str = arr.join(''); // Java

9. Concat

Concat an Array with arguments.

var array = [1,2,3,4,5];

var newArray =  array.concat(1,2,3, [12,12,34], undefined, null);

newArray; // [1, 2, 3, 4, 5, 1, 2, 3, 12, 12, 34, undefined, null]

10. Reverse

Reverse the elements of the array.

var foods =  ["🍎", "🍊", "🍗", "🍕", "🥩"];

foods.reverse();

foods; // ["🥩", "🍕", "🍗", "🍊", "🍎"]

Tip: Reversing string.

var str = "Anitha";

var strArray = [...str].reverse().join('');

11. indexOf

First index of a given element in the Array, if it is not present, it returns -1.

var foods = ["🍎", "🍊", "🍗", "🍕", "🥩", "🍎"];

foods.indexOf('🍎'); // 0

foods.indexOf('🍔'); // -1

12. Some

Checks if any of the elements return true from the callback function.

var num = [1,2,3,4,10, 12];

num.some(n => n > 10); // true

num.some(n => n > 100); // false

13. Every

Check if all of the elements return true from the callback function.

var num = [1,2,3,4,10, 12];

num.every(n => n > 10); // false

num.every(n => n > 0); // true

14. Sort

Sort the elements of the array. By default, it sorts based on char code. We can also pass our sort function.

var arr = ['b', 'c', 'd', 'e'];

arr.sort(); // ["b", "c", "d", "e"]

// custom sort

var arr = [1,2,3,4,5, 11 ];

arr.sort( (a, b) => a-b ); // [1, 2, 3, 4, 5, 11]

Be careful using the sort method, because it sorts based on char code, in which “11" < “2”.

var arr = [1,2,3,4,5, 11 ];

arr.sort();  [1, 11, 2, 3, 4, 5]

Tip: Shuffle an Array with sort.

var arr = [1,2,4,1,2,3];

arr.sort( () => Math.random() - 0.5);

15. Reduce

The reduce() method executes a reducer function (which you provide) on each element of the array, resulting in a single output value.

Example one:

var apples = ["🍎", "🍎"];

var juice = 🧃 ;  // think as empty can 

function makeJuice(juice, fruit) {

    let fruitMix = grind(fruit);
		
    return fruitMix + juice;
		
}

apples.reduce( makeJuice , juice);

Example two:

var arr = [1,2,3,4,5];

var result = 0;

function add(res, currentNum) {
   return res + currentNum;
	 
}

arr.reduce(add, result);

16. ReduceRight

Similar to reduce but elements are passed to the callback function from right to left.

var array = [1,2,3,4,5];

function sum(result, num) {

   console.log(num);
	 
   return result + num;
	 
}

var result = 0;

array.reduce(sum, result);

// go from left to right i.e., 1,2,3,4,5

array.reduceRight(sum, result);

// go from right to left i.r., 5,4,3,2,1

17. Map

Creates a new Array from the value returned by the callback function, which is executed for every element of the Array.

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

function double(num) {
   return num * num;
}

var doubledNumbers = numbers.map(double) 

18. Splice

The splice() method will remove n number of elements from the specific index and also inserts the elements.

var array = [1,2,4,5];

array.splice(2, 0, 3); //insert 3 at index 2

array;  // [1,2,3,4,5]

array.splice(2, 1, 30);//remove 1 item from index 2 and insert 30

array; // [1, 2, 30, 4, 5]

Tip: Use this method to inset an element at a specific index.

function insertElementAtIndex(array, index, elem) {
   array.splice(index, 0, elem);
}

19. Slice

The slice() method returns a shallow copy of a portion of an Array.

var array = [1,2,3,4,5];

array.slice(1); // [2, 3, 4, 5] --> slice starts from index 1 to end

array.slice(1,3); // [2,3]--> slice from index 1 to (3-1)

Tip: Get last element of the array:

// get last n elements

array.slice(-n);

n = 1

array.slice(-1); 5

if n = 3

array.slice(-3); //  [3, 4, 5];

20. forEach

Executes a callback function once for each Array element. We cannot use break and continue in forEach, map functions.

var numbers = [1,2,3,4,5]

numbers.forEach((e) => {

  console.log(e)
	
});

Thank you for reading !

#JavaScript #Arrays #Tips #ES6 #Programming

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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  

---

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 compound assignment operators

JavaScript is unarguablly one of the most common things you’ll learn when you start programming for the web. Here’s a small post on JavaScript compound assignment operators and how we use them.

The compound assignment operators consist of a binary operator and the simple assignment operator.

The binary operators, work with two operands. For example a+b where + is the operator and the a, b are operands. Simple assignment operator is used to assign values to a variable(s).

It’s quite common to modify values stored in variables. To make this process a little quicker, we use compound assignment operators.

They are:

• +=
• -+
• *=
• /=

You can also check my video tutorial compound assignment operators.

Let’s consider an example. Suppose price = 5 and we want to add ten more to it.

var price = 5;
price = price + 10;

We added ten to price. Look at the repetitive price variable. We could easily use a compound += to reduce this. We do this instead.

price += 5;

Awesome. Isn’t it? What’s the value of price now? Practice and comment below. If you don’t know how to practice check these lessons.

Lets bring down the price by 5 again and display it.
We use console.log command to display what is stored in the variable. It is very help for debugging.
Debugging let’s you find errors or bugs in your code. More on this later.

price -= 5;
console.log(price);

Lets multiply price and show it.

price *=5;
console.log(price);

and finally we will divide it.

price /=5;
console.log(price);

If you have any doubts, comment below.

#javascript #javascript compound assignment operators #javascript binary operators #javascript simple assignment operator #doers javascript

20 Fastest Methods to Easily identify Array's Operation in JavaScript

Methods to Get to Know JavaScript Array Operations

For example, Let’s create an Array.

var foods =  ["🍎", "🍊", "🍗", "🍕", "🥩"];

1. Filter

The filter() method creates a new array with elements that return true from the callback function.

var foods =  ["🍎", "🍊", "🍗", "🍕", "🥩"];

var vegFoods = foods.filter( (food) => isVeg(food) );

vegFoods; ["🍎", "🍊", "🍕"];

2. lastIndexOf

First last index of a given element in the Array, if it is not present, it returns -1.

var foods = ["🍎", "🍊", "🍗", "🍕", "🥩", "🍎"];

foods.lastIndexOf('🍎'); // 5

foods.lastIndexOf('🍔'); // -1

3. Length

Returns the number of an element of the Array.

foods.length; // 5

Tip: We can change the length property to delete elements.

foods.length = 0;

foods; // []

4. Push

Add an element to the end of an Array.

var foods =  ["🍎", "🍊", "🍗", "🍕", "🥩"];

foods.push('🍇');

foods; // ["🍎", "🍊", "🍗", "🍕", "🥩", "🍇"]

Tip: Use push with the spread operator (…) as an alternative to the concat method.

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

var num2 = [6,7,8,9,10];

numbers.push(...num2);

5. Unshift

Add an element to the beginning of an Array.

var foods =  ["🍎", "🍊", "🍗", "🍕", "🥩"];

foods.unshift('🍇');

foods; // ["🍇", "🍎", "🍊", "🍗", "🍕", "🥩"]

Tip: Use unshift with the spread operator (…) to concat elements at the beginning.

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

var num2 = [6,7,8,9,10];

numbers.unshift(...num2);

6. Pop

Removes the last element of the array.

var foods =  ["🍎", "🍊", "🍗", "🍕", "🥩"];

foods.pop();  // "🥩"

foods; // ["🍎", "🍊", "🍗", "🍕"]

Tip: We can use the pop method in stack implementation.

7. Shift

Remove the first element of the array.

var foods =  ["🍎", "🍊", "🍗", "🍕", "🥩"];

foods.shift();  // "🍎"

foods; // ["🍊", "🍗", "🍕", "🥩"]

Tip: We can use the shift method in dequeue operations on Queue implementation.

8. Join

Joins the elements of Array to String.

var foods =  ["🍎", "🍊", "🍗", "🍕", "🥩"];

var joinedFood = foods.join(); // "🍎,🍊,🍗,🍕,🥩";

var joinedFood1 = foods.join('--'); // "🍎--🍊--🍗--🍕--🥩"

Tip: Use as an alternative to string concatenation.

var arr = ['J','a','v', 'a'];

var str = '';

// without join

for(let i = 0, len = arr.length; i < len ; i++) {

     str += arr[i];
		 
}

// with join

str = arr.join(''); // Java

9. Concat

Concat an Array with arguments.

var array = [1,2,3,4,5];

var newArray =  array.concat(1,2,3, [12,12,34], undefined, null);

newArray; // [1, 2, 3, 4, 5, 1, 2, 3, 12, 12, 34, undefined, null]

10. Reverse

Reverse the elements of the array.

var foods =  ["🍎", "🍊", "🍗", "🍕", "🥩"];

foods.reverse();

foods; // ["🥩", "🍕", "🍗", "🍊", "🍎"]

Tip: Reversing string.

var str = "Anitha";

var strArray = [...str].reverse().join('');

11. indexOf

First index of a given element in the Array, if it is not present, it returns -1.

var foods = ["🍎", "🍊", "🍗", "🍕", "🥩", "🍎"];

foods.indexOf('🍎'); // 0

foods.indexOf('🍔'); // -1

12. Some

Checks if any of the elements return true from the callback function.

var num = [1,2,3,4,10, 12];

num.some(n => n > 10); // true

num.some(n => n > 100); // false

13. Every

Check if all of the elements return true from the callback function.

var num = [1,2,3,4,10, 12];

num.every(n => n > 10); // false

num.every(n => n > 0); // true

14. Sort

Sort the elements of the array. By default, it sorts based on char code. We can also pass our sort function.

var arr = ['b', 'c', 'd', 'e'];

arr.sort(); // ["b", "c", "d", "e"]

// custom sort

var arr = [1,2,3,4,5, 11 ];

arr.sort( (a, b) => a-b ); // [1, 2, 3, 4, 5, 11]

Be careful using the sort method, because it sorts based on char code, in which “11" < “2”.

var arr = [1,2,3,4,5, 11 ];

arr.sort();  [1, 11, 2, 3, 4, 5]

Tip: Shuffle an Array with sort.

var arr = [1,2,4,1,2,3];

arr.sort( () => Math.random() - 0.5);

15. Reduce

The reduce() method executes a reducer function (which you provide) on each element of the array, resulting in a single output value.

Example one:

var apples = ["🍎", "🍎"];

var juice = 🧃 ;  // think as empty can 

function makeJuice(juice, fruit) {

    let fruitMix = grind(fruit);
		
    return fruitMix + juice;
		
}

apples.reduce( makeJuice , juice);

Example two:

var arr = [1,2,3,4,5];

var result = 0;

function add(res, currentNum) {
   return res + currentNum;
	 
}

arr.reduce(add, result);

16. ReduceRight

Similar to reduce but elements are passed to the callback function from right to left.

var array = [1,2,3,4,5];

function sum(result, num) {

   console.log(num);
	 
   return result + num;
	 
}

var result = 0;

array.reduce(sum, result);

// go from left to right i.e., 1,2,3,4,5

array.reduceRight(sum, result);

// go from right to left i.r., 5,4,3,2,1

17. Map

Creates a new Array from the value returned by the callback function, which is executed for every element of the Array.

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

function double(num) {
   return num * num;
}

var doubledNumbers = numbers.map(double) 

18. Splice

The splice() method will remove n number of elements from the specific index and also inserts the elements.

var array = [1,2,4,5];

array.splice(2, 0, 3); //insert 3 at index 2

array;  // [1,2,3,4,5]

array.splice(2, 1, 30);//remove 1 item from index 2 and insert 30

array; // [1, 2, 30, 4, 5]

Tip: Use this method to inset an element at a specific index.

function insertElementAtIndex(array, index, elem) {
   array.splice(index, 0, elem);
}

19. Slice

The slice() method returns a shallow copy of a portion of an Array.

var array = [1,2,3,4,5];

array.slice(1); // [2, 3, 4, 5] --> slice starts from index 1 to end

array.slice(1,3); // [2,3]--> slice from index 1 to (3-1)

Tip: Get last element of the array:

// get last n elements

array.slice(-n);

n = 1

array.slice(-1); 5

if n = 3

array.slice(-3); //  [3, 4, 5];

20. forEach

Executes a callback function once for each Array element. We cannot use break and continue in forEach, map functions.

var numbers = [1,2,3,4,5]

numbers.forEach((e) => {

  console.log(e)
	
});

Thank you for reading !

#JavaScript #Arrays #Tips #ES6 #Programming

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