Python Arrays

Python provides multiple ways to work with linear data structures, which store elements sequentially. Although Python does not have a built-in array type like some other languages, similar functionality can be achieved using:

• Lists
• Array module
• NumPy arrays

Python Lists

Lists are a flexible and commonly used data structure for storing elements in sequence. Unlike arrays in other languages, list:

• Can store mixed data types in one list
• Elements can be added or removed easily
• Provide functions like append(), remove(), sort(), etc.

a = [1, "Hello", [3.14, "world"]]
a.append(2)  # Add an integer to the end
print(a)  

[1, 'Hello', [3.14, 'world'], 2]

Note: Python does not have built-in arrays like some languages, but similar functionality is available using the array module for storing uniform data types.

NumPy Arrays

NumPy arrays are a part of the NumPy library, which is a tool for numerical computing. Designed for high-performance operations on large datasets and support multi-dimensional arrays and matrices, making them suitable for complex mathematical computations.

• Multi-dimensional support: Can handle multiple dimensions, making them suitable for matrix operations and advanced mathematical tasks.
• Broad broadcasting capabilities: Allow operations between arrays of different shapes and sizes using broadcasting.
• Efficient storage and processing: Uses optimized memory and provide faster performance compared to lists for numerical operations.

import numpy as np
a = np.array([1, 2, 3, 4])

# Element-wise operations
print(a * 2)  

# Multi-dimensional array
res = np.array([[1, 2], [3, 4]])
print(res * 2)

[2 4 6 8]
[[2 4]
 [6 8]]

Note: Use NumPy arrays for complex, multi-dimensional computations. Use Python’s array module for simple, memory-efficient storage of uniform data.

Python Arrays

Array is a collection of elements stored at contiguous memory locations, used to hold multiple values of the same data type. Unlike Lists, which can store mixed types, arrays are homogeneous and require a typecode during initialization to define the data type.

import array as arr
a = arr.array('i', [1, 2, 3])

# accessing First Araay
print(a[0])

# adding element to array
a.append(5)
print(a)  

1
array('i', [1, 2, 3, 5])

Explanation: parameter 'i' is the typecode, it tells Python to treat the elements as signed integers ([1, 2, 3]) of a specific byte size (usually 2 or 4 bytes).

The following table outlines standard typecodes, their mapped C types and minimum memory requirements:

Create an Array

Array can be created by importing an array module. array(data_type, value_list) is used to create array with data type and value list specified in its arguments.

import array as arr
a = arr.array('i', [1, 2, 3])

for i in range(0, 3):
    print(a[i], end=" ")

1 2 3 

Adding Elements to an Array

Elements can be added to an array using insert() to place a value at a specific index, or append() to add a value at the end.

import array as arr
a = arr.array('i', [1, 2, 3])
print(*a)

a.insert(1, 4)  # Insert 4 at index 1
print(*a)

1 2 3
1 4 2 3

Note: We have used *a and *b for unpacking the array elements.

Accessing Array Items

Array elements are accessed using their index with square brackets [ ]. Each item has a position starting from 0 and the index must be an integer.

import array as arr
a = arr.array('i', [1, 2, 3, 4, 5, 6])

print(a[0])
print(a[3])

b = arr.array('d', [2.5, 3.2, 3.3])
print(b[1])
print(b[2])

1
4
3.2
3.3

Removing Elements from the Array

Elements can be removed using remove(), which deletes the first occurrence of a value, or pop(), which removes and returns an element (last by default or a specific index if provided).

import array
a = array.array('i', [1, 2, 3, 1, 5])

# remove first occurance of 1
a.remove(1)
print(a)

# remove item at index 2
a.pop(2)
print(a)

array('i', [2, 3, 1, 5])
array('i', [2, 3, 5])

Slicing of an Array

Slicing is used to access a specific range of elements from an array using index positions.

• Elements from beginning to a range use [:Index]
• Elements from end use [:-Index]
• Elements from specific Index till the end use [Index:]
• Elements within a range, use [Start Index:End Index]
• Print complete List, use [:].
• For Reverse list, use [::-1].

import array as arr
a = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
b = arr.array('i', a)

res = b[3:8]
print(res)

res = b[5:]
print(res)

res = b[:]
print(res)

array('i', [4, 5, 6, 7, 8])
array('i', [6, 7, 8, 9, 10])
array('i', [1, 2, 3, 4, 5, 6, 7, 8, 9, 10])

Searching Element in an Array

In order to search an element in the array we use index() method. This function returns the index of the first occurrence of value mentioned in arguments.

import array
a = array.array('i', [1, 2, 3, 1, 2, 5])

# index of 1st occurrence of 2
print(a.index(2))

# index of 1st occurrence of 1
print(a.index(1))

1
0

Updating Elements in an Array

In order to update an element in the array we simply reassign a new value to the desired index we want to update.

import array
a = array.array('i', [1, 2, 3, 1, 2, 5])

# update item at index 2
a[2] = 6
print(a)

# update item at index 4
a[4] = 8
print(a)

array('i', [1, 2, 6, 1, 2, 5])
array('i', [1, 2, 6, 1, 8, 5])

Arrays Operations

1. Counting Elements in an Array: We can use count() method to count given item in array.

import array
a = array.array('i', [1, 2, 3, 4, 2, 5, 2])

count = a.count(2)
print(count)

3

2. Reversing Elements in an Array: In order to reverse elements of an array use reverse method.

import array
a = array.array('i', [1, 2, 3, 4, 5])

a.reverse()
print(*a)

5 4 3 2 1

3. Extend Element from Array: extend() function is used to attach an item from iterable to the end of the array. This method is used to add an array of values to the end of a given or existing array.

import array as arr 
a = arr.array('i', [1, 2, 3,4,5])

a.extend([6,7,8,9,10])
print(a)

array('i', [1, 2, 3, 4, 5, 6, 7, 8, 9, 10])

Recommended Problems: Rotate Array I, Missing and Repeating in Array, Missing Ranges of Numbers, Reverse Array in Groups, Rotate Array II

Related Links:

• Array vs List
• Common elements in two Arrays
• Pass an Array to a Function
• Create String Array