Introduction to Numpy - Array Indexing and Slicing

Program 1

Array Indexing and Slicing

Python 3.11 Ready

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Mathematical Problem Formulation

1D Array

Program 2

Array Indexing and Slicing

Python 3.11 Ready

import numpy as np

# Create a 2D NumPy array (3x4)
arr = np.array([[10, 20, 30, 40],
                [50, 60, 70, 80],
                [90, 100, 110, 120]])

# Indexing - accessing specific elements
first_element = arr[0, 0]       # Element at first row, first column
middle_element = arr[1, 2]      # Element at second row, third column (70)
last_element = arr[2, 3]        # Element at third row, fourth column (120)

# Slicing - accessing multiple elements
slice_row_1 = arr[0, :]         # All elements of the first row
slice_column_2 = arr[:, 1]      # All elements of the second column
slice_1 = arr[0:2, 1:3]         # First two rows and columns 1 to 2
slice_2 = arr[1:, 2:]           # From second row to the end, and columns 2 to end
slice_step = arr[::2, ::2]      # Every second row and second column
reverse_array = arr[::-1, ::-1] # Reverse rows and columns

# More complex slicing
row_1_column_1_and_3 = arr[0, [1, 3]]  # Elements from the first row, second and fourth column
row_2_and_3_column_1_and_3 = arr[[1, 2], [1, 3]] # Elements at positions (1,1) and (2,3)

# Output the results
print("Original array:\n", arr)
print("\nIndexing:")
print("\nFirst element (arr[0, 0]):\n", first_element)
print("\nMiddle element (arr[1, 2]):\n", middle_element)
print("\nLast element (arr[2, 3]):\n", last_element)

print("\nSlicing:")
print("\nAll elements of the first row (arr[0, :]):\n", slice_row_1)
print("\nAll elements of the second column (arr[:, 1]):\n", slice_column_2)
print("\nFirst two rows and columns 1 to 2 (arr[0:2, 1:3]):\n", slice_1)
print("\nFrom second row onwards and columns 2 onwards (arr[1:, 2:]):\n", slice_2)
print("\nEvery second row and column (arr[::2, ::2]):\n", slice_step)
print("\nReversed array (rows and columns reversed):\n", reverse_array)

print("\nAdvanced Slicing:")
print("\nElements from first row, columns 2 and 4 (arr[0, [1, 3]]):\n", row_1_column_1_and_3)
print("\nElements at positions (1,1) and (2,3) (arr[[1, 2], [1, 3]]):\n", row_2_and_3_column_1_and_3)

Click "Run Code" to execute script and render figures.

Mathematical Problem Formulation

2D Array

Ch. 7.5 Array Indexing and Slicing

Array Indexing and Slicing

Mathematical Problem Formulation

Array Indexing and Slicing

Mathematical Problem Formulation