Array Indexing and Slicing: Program 1

1D Array

import numpy as np # Create a 1D NumPy array arr = np.array([10, 20, 30, 40, 50, 60, 70, 80]) # Indexing - accessing elements first_element = arr[0] # First element last_element = arr[-1] # Last element third_element = arr[2] # Third element # Slicing - accessing multiple elements slice_1 = arr[2:5] # Elements from index 2 to 4 slice_2 = arr[:4] # First 4 elements slice_3 = arr[4:] # Elements from index 4 to the end slice_4 = arr[::2] # Every second element reverse_array = arr[::-1] # Reverse the array # Output the results print("\nOriginal array: \n", arr) print("\nFirst element: \n", first_element) print("\nLast element:\n", last_element) print("\nThird element:\n", third_element) print("\nSlice (2:5):\n", slice_1) print("\nSlice (:4):\n", slice_2) print("\nSlice (4:):\n", slice_3) print("\nSlice with step 2 (every second element):\n", slice_4) print("\nReversed array:\n", reverse_array) Run Code

Output 1

Array Indexing and Slicing: Program 2

2D Array

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) Run Code

Output 2