Indexing and Slicing Arrays

After creating an array, you’ll often need to access individual elements or extract specific sections.

This process is called indexing and slicing.

Indexing retrieves individual items based on their position.

Like Python lists, NumPy arrays use zero-based indexing — the first element is at position 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 allows you to select a range of elements using the : operator.

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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]