Python:NumPy .argmax()

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Priyanshjain10
Published Oct 31, 2025
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The .argmax() method returns the indices of the maximum values along a specified axis in a NumPy ndarray.

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Syntax

ndarray.argmax(axis=None, out=None, *, keepdims=False)

Parameters:

  • axis (int, optional): Axis along which to find the maximum value; flattens the array if None.
  • out (ndarray, optional): Output array to store the result; must match the expected shape.
  • keepdims (bool, optional): If True, retains reduced dimensions with size 1.

Return value:

Returns an integer or ndarray of integers indicating the indices of the maximum values.

Example 1: Finding Maximum Index in 1D Array

In this example, the .argmax() method returns the index of the maximum value in a one-dimensional array:

import numpy as np


arr = np.array([3, 1, 4, 1, 5, 9, 2])
max_index = arr.argmax()


print("Array:", arr)
print("Index of maximum value:", max_index)
print("Maximum value:", arr[max_index])

The output of this code is:

Array: [3 1 4 1 5 9 2]
Index of maximum value: 5
Maximum value: 9

Example 2: Finding Maximum Indices Along Axis in 2D Array

In this example, the .argmax() method finds the indices of maximum values along each axis in a two-dimensional array:

import numpy as np


matrix = np.array([[1, 5, 3],
                   [9, 2, 8],
                   [4, 7, 6]])


# Maximum index along axis 0 (columns)
max_col = matrix.argmax(axis=0)


# Maximum index along axis 1 (rows)
max_row = matrix.argmax(axis=1)


print("Matrix:")
print(matrix)
print("\nMax indices along axis 0 (columns):", max_col)
print("Max indices along axis 1 (rows):", max_row)

The output of this code is:

Matrix:
[[1 5 3]
 [9 2 8]
 [4 7 6]]


Max indices along axis 0 (columns): [1 2 1]
Max indices along axis 1 (rows): [1 0 1]

Example 3: Flattened Array Maximum

In this example, the .argmax() method returns the index of the maximum element from the flattened version of the array:

import numpy as np


matrix = np.array([[10, 25, 15],
                   [30, 20, 35]])


# Find index in flattened array
flat_max_index = matrix.argmax()


print("Matrix:", matrix)
print("Index of maximum in flattened array:", flat_max_index)
print("Maximum value:", matrix.flat[flat_max_index])

The output of this code is:

Matrix: [[10 25 15]
 [30 20 35]]
Index of maximum in flattened array: 5
Maximum value: 35

Codebyte Example

In this example, the .argmax() method identifies the student with the highest score using their index position:

Code
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  • Career path
    Data Scientist: Machine Learning Specialist
    Machine Learning Data Scientists solve problems at scale, make predictions, find patterns, and more! They use Python, SQL, and algorithms.
    • Includes 27 Courses
    • With Professional Certification
    • Beginner Friendly.
      95 hours
  • Course
    Learn Python 3
    Learn the basics of Python 3.12, one of the most powerful, versatile, and in-demand programming languages today.

    • With Certificate
    • Beginner Friendly.
      24 hours