NumPy - nonzero() function

The NumPy nonzero() function returns the indices of the elements that are non-zero. Returned value is a tuple of arrays, one for each dimension of a, containing the indices of the non-zero elements in that dimension. The values in a are always tested and returned in row-major, C-style order.

Syntax

numpy.nonzero(a)

Parameters

`a`	`Required.` Specify the input array (array_like).

Return Value

Returns the indices of elements that are non-zero.

Example:

In the example below, nonzero() function is used to find out index of all elements which are non-zero.

import numpy as np
Arr = np.array([10, 20, 0, 0, 50, 0, 70])

print("Array is:")
print(Arr)

#index of all elements which are non-zero
x = np.nonzero(Arr)
print("\nIndices of nonzero elements:")
print(x)

#displaying all nonzero elements
print("\nAll nonzero elements:")
print(Arr[x])

The output of the above code will be:

Array is:
[10 20  0  0 50  0 70]

Indices of nonzero elements:
(array([0, 1, 4, 6]),)

All nonzero elements:
[10 20 50 70]

Example:

Similarly, nonzero elements from a 2-D array can be found out using nonzero() function.

import numpy as np
Arr = np.array([[1, 2, 0], 
                [0, 5, 0], 
                [7, 0, 9]])

print("Array is:")
print(Arr)

#index of all elements which are non-zero
x = np.nonzero(Arr)
print("\nIndices of nonzero elements:")
print(x)

#displaying all nonzero elements
print("\nAll nonzero elements:")
print(Arr[x])

The output of the above code will be:

Array is:
[[1 2 0]
 [0 5 0]
 [7 0 9]]

Indices of nonzero elements:
(array([0, 0, 1, 2, 2]), array([0, 1, 1, 0, 2]))

All nonzero elements:
[1 2 5 7 9]

Example:

A condition can be applied to nonzero() function as shown in the example below.

import numpy as np
Arr = np.array([90, 80, 10, 20, 50])

print("Array is:")
print(Arr)

#index of all elements which are greater than 25
x = np.nonzero(Arr > 25)
print("\nIndices of elements greater than 25:")
print(x)

#displaying all elements greater than 25
print("\nAll elements greater than 25:")
print(Arr[x])

The output of the above code will be:

Array is:
[90 80 10 20 50]

Indices of elements greater than 25:
(array([0, 1, 4]),)

All elements greater than 25:
[90 80 50]

❮ NumPy - Functions