Indexing and Slicing Arrays

After creating an array, you often need to access specific elements or select parts of it.

This is done with indexing and slicing.

Indexing retrieves one item using its position.

Like Python lists, NumPy arrays start at index 0.

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arr = np.array([10, 20, 30, 40])
print(arr[1])  # Output: 20

For 2D arrays, use two indices: arr[row, column].

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matrix = np.array([[1, 2], [3, 4]])
print(matrix[1, 0])  # Output: 3

Slicing selects a range of values using : notation.

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arr = np.array([10, 20, 30, 40, 50])
print(arr[1:4])  # Output: [20 30 40]

You can also slice rows or columns in 2D arrays.

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matrix = np.array([[1, 2, 3], [4, 5, 6]])
print(matrix[:, 1])  # Output: [2 5]