1596992400

# Count of Array elements greater than all elements on its left

Given an array arr[], the task is to print the number of elements which are greater than all the elements on its left as well as greater than the next K elements on its right.

Examples:

_Input: _arr[] = { 4, 2, 3, 6, 4, 3, 2}, K = 2

_Output: _2

Explanation:

arr[0](= 4): arr[0] is the 1st element in the array and greater than its next K(= 2) elements {2, 3}.

arr[2](= 6): arr[2] is greater than all elements on its left {4, 2, 3} and greater than its next K(= 2) elements {4, 3}.

Therefore, only two elements satisfy the given condition.

_Input: _arr[] = { 3, 1, 2, 7, 5, 1, 2, 6}, K = 2

_Output: _2

Naive Approach:

Traverse over the array and for each element, check if all elements on its left are smaller than it as well as the next K elements on its right are smaller than it. For every such element, increase count. Finally, print count.

Time Complexity:_ O(N2)_

Auxiliary Space:_ O(1)_

Efficient Approach:

The above approach can be optimized by using the Stack Data Structure. Follow the steps below to solve the problem:

1. Initialize a new array and store the index of the Next Greater Element for each array element using Stack.
2. Traverse the given array and for each element, check if it is maximum obtained so far and its next greater element is at least K indices after the current index. If found to be true, increase** count**.
3. Finally, print count.

Below is the implementation of the above approach:

• C++

`// C++ Program to implement`

`// the above approach`

`#include <bits/stdc++.h>`

`**using**` `**namespace**` `std;`

`// Function to print the count of`

`// Array elements greater than all`

`// elemnts on its left and next K`

`// elements on its right`

`**int**` `countElements(``**int**` `arr[],` `**int**` `n,`

`**int**` `k)`

`{`

`stack<``**int**``> s;`

`vector<``**int**``> next_greater(n, n + 1);`

`// Iterate over the array`

`**for**` `(``**int**` `i = 0; i < n; i++) {`

`**if**` `(s.empty()) {`

`s.push(i);`

`**continue**``;`

`}`

`// If the stack is not empty and`

`// the element at the top of the`

`// stack is smaller than arr[i]`

`**while**` `(!s.empty()`

`&& arr[s.top()] < arr[i]) {`

`// Store the index of next`

`// greater element`

`next_greater[s.top()] = i;`

`// Pop the top element`

`s.pop();`

`}`

`// Insert the current index`

`s.push(i);`

`}`

`// Stores the count`

`**int**` `count = 0;`

`**int**` `maxi = INT_MIN;`

`**for**` `(``**int**` `i = 0; i < n; i++) {`

`**if**` `(next_greater[i] - i > k`

`&& maxi < arr[i]) {`

`maxi = max(maxi, arr[i]);`

`count++;`

`}`

`}`

`**return**` `count;`

`}`

`// Driver Code`

`**int**` `main()`

`{`

`**int**` `arr[] = { 4, 2, 3, 6, 4, 3, 2 };`

`**int**` `K = 2;`

`**int**` `n =` `**sizeof**``(arr) /` `**sizeof**``(arr[0]);`

`cout << countElements(arr, n, K);`

`**return**` `0;`

`}`

Output:

``````2
``````

Time Complexity:_ O(N)_

Auxiliary Space:_ O(N)_

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.

#arrays #mathematical #searching #stack #python

1666082925

## 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
- 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.

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
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:

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

1670560264

## 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.

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
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:

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

1684293566

## Find the Array Length in Bash

Bash supports both numeric and associative arrays. The total number of elements of these types of arrays can be calculated in multiple ways in Bash. The length of the array can be counted using the “#” symbol or loop, or using a command like “wc” or “grep”.  The different ways of counting the array length in Bash are shown in this tutorial.

## Find the Array Length Using “#”

Using the “#” symbol is the simplest way to calculate the array length. The methods of counting the total number of elements of the numeric and associative array is shown in this part of the tutorial.

## Example 1: Count the Length of a Numeric Array Using “#”

Create a Bash file with the following script that counts and prints the length of a numeric array using the “#” symbol. The “@” and “*” symbols are used here to denote all elements of the array.

``````#Declare a numeric array

items=("Shirt" "T-Shirt" "Pant" "Panjabi" "Shoe")

#Count array length using '#'

echo "Array length using '#' with '@':  \${#items[@]}"

echo "Array length using '#' with '*':  \${#items[*]}"``````

The following output appears after executing the script. The array contains five string values and the same output is shown for both “@” and “*” symbols:

## Example 2: Count the Length of an Associative Array Using “#”

Create a Bash file with the following script that counts and prints the length of an associative array using the “#” symbol. The “@” and “*” symbols are used here to denote all elements of the array.

``````#Declare an associative array

declare -A items=([6745]="Shirt (M)" [2345]="Shirt (L)" [4566]="Pant (36)")

#Count array length using '#'

echo "Associative array length using '#' with '@':  \${#items[@]}"

echo "Associative array length using '#' with '*':  \${#items[*]}"``````

The following output appears after executing the script. The array contains three string values and the same output is shown for both the “@” and “*” symbols:

## Find the Array Length Using a Loop

Using a loop is another way to count the total number of elements in the array. The length of an array is counted using a while loop in the following example:

## Example: Count the Length of an Array Using a Loop

Create a Bash file with the following script that counts the total number of elements using a “while” loop. A numeric array of four string values is declared in the script using the “declare” command. The “for” loop is used to iterate and print the values of the array. Here, the \$counter variable is used to count the length of the array that is incremented in each iteration of the loop.

``````#Declare an array

declare -a items=("Shirt(M)" "Shirt(L)" "Panjabi(42)" "Pant(38)")

echo "Array values are:"

#Count array length using loop

counter=0

#Iterate the array values

for val in \${items[@]}

do

#Print the array value

echo \$val

((counter++))

done

echo "The array length using loop is \$counter."``````

The following output appears after executing the script. The array values and the length of the array are printed in the output:

## Find the Array Length Using the “Wc” Command

The length of the array can be counted using some commands. The “wc” command is one of them. But this command does not return the correct output if the array contains the string value of multiple words. The method of counting the total number of elements of an array and comparing the array length value that is counted by the “#” symbol and “wc” command is shown in the following example.

## Example: Count the Length of an Array Using the “Wc” Command

Create a Bash file with the following script that counts the total number of elements using the “wc” command. A numeric array of five string values is declared in the script. The “wc” command with the -w option is used to count the length of two arrays of 5 elements. One array contains a string of one word and another array contains a string of two words. The length of the second arrays is counted using the “#” symbol and the “wc” command.

``````#Declare a numeric array of a single word of the string

items=("Shirt" "T-Shirt" "Pant" "Panjabi" "Shoe")

echo "Array values: \${items[@]}"

#Count array length using 'wc'

len=`echo \${items[@]} | wc -w`

echo "Array length using 'wc' command: \$len"

#Declare a numeric array of multiple words of the string

items2=("Shirt (XL)" "T-Shirt (L)" "Pant (34)" "Panjabi (38)" "Shoe (9)")

echo "Array values: \${items2[@]}"

echo "Array length using '#': \${#items2[@]}"

#Count array length using 'wc'

len=`echo \${items2[@]} | wc -w`

echo "Array length using 'wc' command: \$len"``````

The following output appears after executing the script. According to the output, the “wc” command generates the wrong output for the array that contains a string value of two words:

## Conclusion

The methods of counting the length of an array using the “#” symbol, loop, and the “wc” command are shown in this tutorial.

Original article source at: https://linuxhint.com/

1684297323

## 在 Bash 中查找数组长度

Bash 支持数字数组和关联数组。在 Bash 中可以通过多种方式计算这些类型数组的元素总数。可以使用“ # ”符号或循环，或使用“ wc”或“grep ”等命令来计算数组的长度。本教程展示了在 Bash 中计算数组长度的不同方法。

## 示例 1：使用“#”计算数值数组的长度

``````#Declare a numeric array

items=("Shirt" "T-Shirt" "Pant" "Panjabi" "Shoe")

#Count array length using '#'

echo "Array length using '#' with '@':  \${#items[@]}"

echo "Array length using '#' with '*':  \${#items[*]}"``````

## 示例 2：使用“#”计算关联数组的长度

``````#Declare an associative array

declare -A items=([6745]="Shirt (M)" [2345]="Shirt (L)" [4566]="Pant (36)")

#Count array length using '#'

echo "Associative array length using '#' with '@':  \${#items[@]}"

echo "Associative array length using '#' with '*':  \${#items[*]}"``````

## 示例：使用循环计算数组的长度

``````#Declare an array

declare -a items=("Shirt(M)" "Shirt(L)" "Panjabi(42)" "Pant(38)")

echo "Array values are:"

#Count array length using loop

counter=0

#Iterate the array values

for val in \${items[@]}

do

#Print the array value

echo \$val

((counter++))

done

echo "The array length using loop is \$counter."``````

## 示例：使用“Wc”命令计算数组的长度

``````#Declare a numeric array of a single word of the string

items=("Shirt" "T-Shirt" "Pant" "Panjabi" "Shoe")

echo "Array values: \${items[@]}"

#Count array length using 'wc'

len=`echo \${items[@]} | wc -w`

echo "Array length using 'wc' command: \$len"

#Declare a numeric array of multiple words of the string

items2=("Shirt (XL)" "T-Shirt (L)" "Pant (34)" "Panjabi (38)" "Shoe (9)")

echo "Array values: \${items2[@]}"

echo "Array length using '#': \${#items2[@]}"

#Count array length using 'wc'

len=`echo \${items2[@]} | wc -w`

echo "Array length using 'wc' command: \$len"``````

1684301100

## Найдите длину массива в Bash

Bash поддерживает как числовые, так и ассоциативные массивы. Общее количество элементов этих типов массивов может быть вычислено несколькими способами в Bash. Длину массива можно подсчитать с помощью символа « # » или цикла, или с помощью команды типа « wc» или «grep ». В этом руководстве показаны различные способы подсчета длины массива в Bash.

## Найдите длину массива, используя «#»

Использование символа « # » — самый простой способ вычислить длину массива. В этой части руководства показаны способы подсчета общего количества элементов числового и ассоциативного массива.

## Пример 1. Подсчет длины числового массива с использованием «#»

Создайте файл Bash со следующим сценарием, который подсчитывает и печатает длину числового массива, используя символ «#». Здесь используются символы «@» и «* » для обозначения всех элементов массива.

``````#Declare a numeric array

items=("Shirt" "T-Shirt" "Pant" "Panjabi" "Shoe")

#Count array length using '#'

echo "Array length using '#' with '@':  \${#items[@]}"

echo "Array length using '#' with '*':  \${#items[*]}"``````

Следующий вывод появляется после выполнения скрипта. Массив содержит пять строковых значений, и для символов « @» и «* » отображается один и тот же результат :

## Пример 2. Подсчет длины ассоциативного массива с использованием «#»

Создайте файл Bash со следующим сценарием, который подсчитывает и печатает длину ассоциативного массива, используя символ «#». Здесь используются символы «@» и «* » для обозначения всех элементов массива.

``````#Declare an associative array

declare -A items=([6745]="Shirt (M)" [2345]="Shirt (L)" [4566]="Pant (36)")

#Count array length using '#'

echo "Associative array length using '#' with '@':  \${#items[@]}"

echo "Associative array length using '#' with '*':  \${#items[*]}"``````

Следующий вывод появляется после выполнения скрипта. Массив содержит три строковых значения, и для символов « @» и «* » отображается один и тот же результат :

## Найдите длину массива с помощью цикла

Использование цикла — еще один способ подсчета общего количества элементов в массиве. Длина массива подсчитывается с помощью цикла while в следующем примере:

## Пример. Подсчет длины массива с использованием цикла

Создайте файл Bash со следующим сценарием, который подсчитывает общее количество элементов с помощью цикла « пока ». Числовой массив из четырех строковых значений объявляется в скрипте с помощью команды « объявить ». Цикл for используется для повторения и печати значений массива. Здесь переменная \$counter используется для подсчета длины массива, который увеличивается на каждой итерации цикла.

``````#Declare an array

declare -a items=("Shirt(M)" "Shirt(L)" "Panjabi(42)" "Pant(38)")

echo "Array values are:"

#Count array length using loop

counter=0

#Iterate the array values

for val in \${items[@]}

do

#Print the array value

echo \$val

((counter++))

done

echo "The array length using loop is \$counter."``````

Следующий вывод появляется после выполнения скрипта. Значения массива и длина массива печатаются в выводе:

## Найдите длину массива с помощью команды «Wc»

Длину массива можно подсчитать с помощью некоторых команд. Команда « wc » — одна из них. Но эта команда не возвращает правильный вывод, если массив содержит строковое значение из нескольких слов. В следующем примере показан метод подсчета общего количества элементов массива и сравнения значения длины массива, подсчитываемого символом « # » и командой « wc ».

## Пример: подсчет длины массива с помощью команды «Wc»

Создайте файл Bash со следующим сценарием, который подсчитывает общее количество элементов с помощью команды « wc ». В скрипте объявлен числовой массив из пяти строковых значений. Команда « wc » с параметром -w используется для подсчета длины двух массивов по 5 элементов. Один массив содержит строку из одного слова, а другой массив содержит строку из двух слов. Длина вторых массивов подсчитывается с помощью символа « # » и команды « wc ».

``````#Declare a numeric array of a single word of the string

items=("Shirt" "T-Shirt" "Pant" "Panjabi" "Shoe")

echo "Array values: \${items[@]}"

#Count array length using 'wc'

len=`echo \${items[@]} | wc -w`

echo "Array length using 'wc' command: \$len"

#Declare a numeric array of multiple words of the string

items2=("Shirt (XL)" "T-Shirt (L)" "Pant (34)" "Panjabi (38)" "Shoe (9)")

echo "Array values: \${items2[@]}"

echo "Array length using '#': \${#items2[@]}"

#Count array length using 'wc'

len=`echo \${items2[@]} | wc -w`

echo "Array length using 'wc' command: \$len"``````

Следующий вывод появляется после выполнения скрипта. Судя по выводу, команда « wc » выдает неверный вывод для массива, содержащего строковое значение из двух слов:

## Заключение

В этом руководстве показаны методы подсчета длины массива с помощью символа « # », цикла и команды « wc ».

Оригинальный источник статьи: https://linuxhint.com/