Array in Python

Definition

• In Python, arrays are collections that store multiple items of the same/different data type depending on the array type used in Python. 

Features

• Unlike C or Java, Python has no built-in array data type. Instead, Python provides alternatives like lists and the array module for arrays.

Types of Array in Python

(A) Lists in Python

• Lists are mutable dynamic structures and can store multiple elements of different data types, making them a common substitute for arrays in Python.
• They are not as memory-efficient as real arrays when dealing with large datasets of uniform type.
• This array is used for basic, flexible data structures and is defined using a [ ] symbol.
• Unlike Tuple, they are mainly used when we want data to change in an application.
• For example –

• Features of Lists:
  • Lists can store multiple elements of different types.
  • The Lists elements are mutable (can change their elements).
  • The Lists can grow or shrink dynamically.
• Common Operations and Methods Associated with the Lists:
  • Accessing the elements
    • print(list1[0])  # Accessing first element: 10
  • Appending an element
    • list1.append(60)  # [10, 20, 30, 40, 50, 60]
  • Inserting at a specific index
    • list1.insert(1, 70)  # [10, 70, 20, 30, 40, 50, 60]
  • Removing elements
    • list1.remove(70)  # [10, 20, 30, 40, 50, 60]
  • Slicing a list
    • print(list1[1:4])  # [20, 30, 40]

(B) Array Module in Python

• Array Module is a basic array that is more memory efficient than lists but requires homogeneous data.
• If we need an actual array in Python, the array module provides an array object that only stores elements of the same data type (e.g., integers, floats).
• For importing the array Module, we use – import array.
• For Examples –

• Features of array Module
  • Arrays are more efficient than lists when working with large collections of the same data type.
  • It requires specifying the type of the array elements using type codes (e.g., ‘i’ for integers, ‘f’ for floats).
• Common Type Codes in Array

• Common Operations with Arrays

• • Accessing elements
    • print(array1[1])  # Second element: 2
  • Appending an element
    • array1.append(6)  # array(‘i’, [1, 2, 3, 4, 5, 6])
  • Inserting at a specific index
    • array1.insert(2, 10)  # array(‘i’, [1, 2, 10, 3, 4, 5, 6])
  • Removing elements
    • array1.remove(10)  # array(‘i’, [1, 2, 3, 4, 5, 6])
• Looping through array

(C) NumPy Arrays (Advanced)

• NumPy is a powerful library for handling large, multi-dimensional arrays with efficient mathematical operations in Python.
• The NumPy library is often used in Python for more efficient and complex array operations.
• NumPy provides multi-dimensional arrays and high-level mathematical functions unavailable in basic lists or the array module.
• This array is used for high-performance numerical computation mainly.
• For Installing NumPy

pip install numpy

• To Create a NumPy Array

• Features of NumPy Arrays
  • Homogeneous: All elements in a NumPy array must be of the same type.
  • Supports multi-dimensional arrays (e.g., 2D arrays or matrices).
  • Optimized for numerical operations, making it much faster than lists for mathematical calculations.
• Common NumPy Operations
  • Accessing elements
    • print(arr[0])  # Output: 1
  • Performing mathematical operations
    • print(arr * 2)  # Element-wise multiplication: [2 4 6 8 10]
• Reshaping arrays: We can convert 1D into 2D as needed using NumPy Arrays.
  • array2 = arr.reshape(5, 1)  # Convert 1D array into 2D array with 5 rows and 1 column

• Matrix multiplication using NumPy Array

import numpy as np

• Definition
  • Tuples in Python are immutable(not change), ordered collections of data items of the same/different type used when the user wants to group related data that should not be modified. 
• Characteristics
  • They are Indexed, i.e. Like lists, tuple elements are accessed using indices starting from 0.
  • They are similar to lists, but unlike lists, tuples cannot be modified after they are created.
  • They are faster in operations((because of immutability) than Lists.
  • They are mainly used when we don’t want data to change in an application.
  • They offer efficient access to data and are often used in cases where immutability is essential, such as returning multiple values from functions or using them as dictionary keys.
• Advantages 
  • Since Tuple is the ordered collection of items hence maintains the order of elements.
  • They are Heterogeneous i.e., Tuples can store elements of different data types (e.g., integers, strings, floats) as needed.
  • Tuples are often used to group related data, and their immutability can be useful when we want to ensure that certain data remains unchanged throughout a program.

• Disadvantages 

• • They are immutable i.e., once a tuple is created, its contents cannot be changed (no adding, removing, or modifying elements). It may be advantageous in a few cases also.

• To Create Tuples

• • We can create a tuple by enclosing values in parentheses `()` and separating them with commas.
  • For example –
    • x = (10, 20, 30, 40, 50)    # Tuple with same data types.
    • y= (10, “Hello India”, 3.141, True)    # Tuple with different data types/mix tuple/hybrid tuple.
    • z= (50,)  # Single element tuple (requires a trailing comma), without the comma, it’s just an integer.
    • k = ()   #Empty tuple
• Accessing Tuple Elements

• • We can access individual elements of a tuple using indexing, or retrieve multiple elements using slicing.
  • For Example:
    • x = (10, 20, 30, 40, 50, 60, 70, 80, 90)

• • • Tuple is Immutable: Since tuples are immutable, we cannot change their content after creation. For example, trying to assign a new value to an index will raise an error. For example:-

• • • Creating and accessing tuple elements

• Tuple Operations
  • Concatenation: We can concatenate two or more tuples using the `+` operator.

• • Repetition: We can repeat the contents of a tuple using the `*` operator.

• • Membership Testing: We can check if an item is present in a tuple using the `in` keyword.

• Tuple Methods

Since tuples are immutable, hence they have comparatively only a few methods than Lists, mainly for querying.

• • count():
    • This method returns the number of occurrences of a specific value in the tuple.
    • For example –

• • index():
    • This method returns the index of the first occurrence of that specified value.
    • For example –

• Packing and Unpacking Tuples
  • Tuple Packing
    • The assignment of multiple values (of different types) to a tuple in a single statement is called packing.
    • For example –

• • Tuple Unpacking
    • We can also unpack a tuple into individual variables.
    • For example – 

• • • Unpacking with a wildcard (`*`): We can use `*` to unpack the remaining values into a list.

• Use of Tuples
  • Return Multiple Values from Functions
    • Tuples are often used to return multiple values from a function.
    • For example –

• • Immutable Grouping of Related Data
    • If we want to group related items and ensure they don’t change, a tuple is used.
    • user_profile = (“Rani”, 18, “Student”)
  • Keys in Dictionaries:
    • Tuples can be used as keys in dictionaries, whereas lists cannot because tuples are immutable and washable.
    • For example – 

   my_dict = {(1, 2): “Point A”, (3, 4): “Point B”}