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All About Arrays

What is an Array?

An Array is a data structure that stores multiple values in a single variable. It’s like container that holds a collection of items in an ordered list.

Key Features:

Elements have a specific position or index
Each element can be accessed by its position (index) number
You can change, add, or remove elements
Usually stores elements of the same data type

Why are Arrays Important?

Arrays allow you to:

Store multiple related values together
Process large amounts of data efficiently
Organize information in a structured way
Perform operations on collections of data

Real-world examples:

List of student grades
Shopping cart items

Arrays in Python

In Python, arrays are called lists.

Tip: Python lists are more flexible than traditional arrays in other languages!

# Example 1: Creating a simple array/list
fruits = ["apple", "banana", "orange", "grape"]
print("Fruits list:", fruits)
print("Type:", type(fruits))

Explanation:

fruits is a list containing 4 string elements
Square brackets [] create a list
Elements are separated by commas
type() shows this is a list object

Array Indexing

Each element in an array has a position number. This is called an index:

Index	Element	Description
0	First	Arrays start at 0
1	Second	Next Position
2	Third	Next Position
-1	Last	Negative indices count backwards

# Array indexing examples
colors = ["red", "blue", "green", "yellow", "purple"]

print("Full array:", colors)
print("\nIndexing examples:")
print("First element (index 0):", colors[0])
print("Second element (index 1):", colors[1])
print("Last element (index -1):", colors[-1])
print("Second to last (index -2):", colors[-2])

Key Indexing Concepts:

Zero-Indexed: Arrays start counting from 0
Negative Indices: -1 is the last element
Direct Access: colors[0] gets first element
Backwards Count: colors[-1] gets last element

Array Operations

Basic Operations:

Add Elements: append(), insert()
Remove Elements: remove(), pop()
Search Elements: in keyword, index()
Get Length: len() function

# Starting with an empty array
shopping_cart = []
print("Empty cart:", shopping_cart)

# Adding elements (append)
shopping_cart.append("milk")
shopping_cart.append("bread")
shopping_cart.append("eggs")
print("After adding items:", shopping_cart)

# Inserting at specific position
shopping_cart.insert(1, "butter")
print("After inserting butter at index 1:", shopping_cart)

# Removing elements
shopping_cart.remove("bread")
print("After removing bread:", shopping_cart)

# Checking if element exists
if "milk" in shopping_cart:
    print("Milk is in the cart!")

Operation Details:

Adding Elements:

append() adds to the end
insert(index, item) adds at specific position

Removing Elements:

remove(item) removes first occurrence
in keyword checks if item exists

Array Slicing

You can get portions of an array using slicing:

Slicing Syntax:

array[start:end]

Examples:

array[:3] - First 3 elements
array[2:6] - Elements from index 2 to 5
array[::2] - Every 2nd element
array[::-1] - Reverse the array

numbers = [10, 20, 30, 40, 50] # let's slice it now!
numbers[1:4] #this will give us [20, 30, 40]. It stops before index 4, so it includes indices 1, 2, and 3, the end index is exclusive.

# Slicing with a step
numbers[0:5:2] # this will give us [10, 30, 50]. It starts at index 0, goes up to (but not including) index 5, and takes every second element.

# Omitting start or end index
numbers[:3] # this will give us [10, 20, 30]. It starts from the beginning and goes up to (but not including) index 3.
numbers[2:] # this will give us [30, 40, 50]. It starts from index 2 and goes to the end of the list.

# Negative indices
numbers[-3:] # this will give us [30, 40, 50]. It starts from the third-to-last element and goes to the end.
numbers[:-2] # this will give us [10, 20, 30]. It goes up to (but not including) the second-to-last element

Arrays inside Arrays

Arrays can contain other arrays, where an element in a data structure is an array itself. These can be known as multi-dimensional arrays.

It’s almost like a spreadsheet:

Student	Math	Science	English
Student 1	85	92	78
Student 2	90	88	95
Student 3	78	85	82

Summary

Key Concepts:

Store Multiple Values in an ordered collection
Zero-Indexed - First element is at position 0
Mutable - Modify, add, and remove elements
Versatile - Support many operations

Essential Operations:

When to Use Arrays:

Storing lists of related data
Processing collections of information
Implementing algorithms with sequences
Managing ordered data that needs indexing

Works Cited

https://github.com/precia-verma/Group-projects/blob/main/_notebooks/Foundation/javascript/Array/2025-09-24-The-Coders-Array-js-Hack.ipynb - Hacks

https://github.com/precia-verma/Group-projects/blob/main/_notebooks/Foundation/javascript/Array/2025-10-03-The-Coders-Array-homework.ipynb - Homework