Python Arrays Complete Guide

# Creating 1D arrays
numbers = [10, 20, 30, 40, 50]
fruits = ["apple", "banana", "cherry"]
mixed = [1, "hello", 3.14, True]  # Python lists can hold different types

# Accessing elements
print("First element:", numbers[0])      # 10
print("Last element:", numbers[-1])      # 50 (negative indexing)
print("Second element:", fruits[1])      # banana

# Modifying elements
numbers[2] = 35       # Change 30 to 35
fruits[0] = "orange"  # Change "apple" to "orange"
print("Modified numbers:", numbers)
print("Modified fruits:", fruits)

# Array length
print("Length of numbers:", len(numbers))      # 5
print("Length of fruits:", len(fruits))        # 3

# Adding elements
numbers.append(60)            # Add to end
numbers.insert(2, 25)         # Insert at index 2
print("After adding:", numbers)

# Removing elements
removed = numbers.pop()       # Remove last element
print("Removed:", removed)
numbers.remove(20)            # Remove first occurrence of 20
print("After removal:", numbers)

# Slicing arrays
print("First 3 elements:", numbers[:3])      # [10, 25, 35]
print("Last 3 elements:", numbers[-3:])      # [35, 40, 50]
print("Elements 1-3:", numbers[1:4])         # [25, 35, 40]
print("Every other element:", numbers[::2])  # [10, 35, 50]

# Array concatenation
array1 = [1, 2, 3]
array2 = [4, 5, 6]
combined = array1 + array2
print("Combined array:", combined)  # [1, 2, 3, 4, 5, 6]

# Array repetition
repeated = [1, 2] * 3
print("Repeated array:", repeated)  # [1, 2, 1, 2, 1, 2]

# Finding elements
if 35 in numbers:
    print("35 found in array at index:", numbers.index(35))

# Counting occurrences
count_array = [1, 2, 3, 2, 1, 2, 3, 2, 1]
print("Count of 2:", count_array.count(2))  # 4

# Creating 2D arrays (lists of lists)
matrix = [
    [1, 2, 3],      # Row 0
    [4, 5, 6],      # Row 1
    [7, 8, 9]       # Row 2
]

# Alternative way to create 2D array
rows, cols = 3, 4
matrix2 = [[0 for _ in range(cols)] for _ in range(rows)]
print("3x4 Zero matrix:", matrix2)

# Accessing elements
print("Element at [0][0]:", matrix[0][0])   # 1
print("Element at [1][2]:", matrix[1][2])   # 6
print("Element at [2][1]:", matrix[2][1])   # 8

# Modifying elements
matrix[0][1] = 20      # Change 2 to 20
matrix[2][2] = 90      # Change 9 to 90
print("Modified matrix:", matrix)

# Array dimensions
print("Number of rows:", len(matrix))                 # 3
print("Number of columns:", len(matrix[0]))           # 3
print("Total elements:", len(matrix) * len(matrix[0])) # 9

# Iterating through 2D array
print("\nMatrix elements:")
for i in range(len(matrix)):          # Loop through rows
    for j in range(len(matrix[i])):   # Loop through columns
        print(f"matrix[{i}][{j}] = {matrix[i][j]}", end="  ")
    print()  # New line after each row

# Using nested loops (alternative)
print("\nUsing nested for-each loops:")
for row in matrix:
    for element in row:
        print(element, end=" ")
    print()

# Adding rows and columns
matrix.append([10, 11, 12])          # Add new row
print("\nAfter adding row:", matrix)

# Add column to each row
for row in matrix:
    row.append(0)                    # Add 0 to each row
print("After adding column:", matrix)

# Slicing 2D arrays
print("\nFirst two rows:", matrix[:2])           # Rows 0-1
print("First two columns of first row:", matrix[0][:2])  # Columns 0-1 of row 0

# Transpose a matrix (using list comprehension)
transpose = [[matrix[j][i] for j in range(len(matrix))] 
             for i in range(len(matrix[0]))]
print("\nTranspose of matrix:")
for row in transpose:
    print(row)

# Real-world example: Student marks
student_marks = [
    ["Alice", 85, 92, 78],
    ["Bob", 72, 88, 91],
    ["Charlie", 95, 89, 94]
]

print("\nStudent Marks Table:")
print("Name\tMath\tScience\tEnglish")
print("-" * 35)
for student in student_marks:
    print(f"{student[0]}\t{student[1]}\t{student[2]}\t{student[3]}")