Get Maximum Value of a Numpy Array along an Axis

Contents

Introduction
Syntax – numpy.amax()
Example 1 – Maximum Value along an Axis
Example 2 – Maximum Value along Multiple Axes
Summary

Maximum Value of a Python Numpy Array along an Axis

You can find the maximum or largest value of a Numpy array, not only in the whole numpy array, but also along a specific axis or set of axes.

To get the maximum value of a Numpy Array along an axis, use numpy.amax() function.

Syntax – numpy.amax()

The syntax of numpy.amax() function is given below.

max_value = numpy.amax(arr, axis)

If you do not provide any axis, the maximum of the array is returned.

You can provide axis or axes along which to operate. If axis is a tuple of integers representing the axes, then the maximum is selected over these specified multiple axes.

Example 1 – Maximum Value along an Axis

In the following example, we will take a numpy array with random numbers and then find the maximum of the array along an axis using amax() function.

We shall find the maximum value along axis=0 and axis=1 separately.

Python Program

import numpy as np

# 2D array => 2 axes
arr = np.random.randint(10, size=(4,5))
print(arr)

#find maximum value along axis=0
amax_value = np.amax(arr, axis=0)
print('Maximum value of the array along axis=0 is:')
print(amax_value)

#find maximum value along axis=1
amax_value = np.amax(arr, axis=1)
print('Maximum value of the array along axis=1 is:')
print(amax_value)

Run

Output

[[4 8 8 9 4]
 [8 5 2 4 0]
 [2 3 3 8 7]
 [6 6 5 0 4]]
Maximum value of the array along axis=0 is:
[8 8 8 9 7]
Maximum value of the array along axis=1 is:
[9 8 8 6]

Example 2 – Maximum Value along Multiple Axes

As already mentioned, we can calculate the maximum value along multiple axes. Provide all the axis, as a tuple, along which you would like to find the maximum value.

Python Program

import numpy as np

# 2D array => 2 axes
arr = np.random.randint(9, size=(2,2,4))
print(arr)

# find maximum value along axis=0,2
amax_value = np.amax(arr, axis=(0, 2))
print('Maximum value of the array along axis=(0,2) is:')
print(amax_value)

Run

Output

[[[5 6 1 2]
  [5 5 3 6]]

 [[5 2 3 3]
  [7 5 7 4]]]
Maximum value of the array along axis=(0,2) is:
[6 7]

Summary

In this Numpy Tutorial of Python Examples, we learned how to find the maximum value of a numpy array along an axis or multiple axes combined.