Python NumPy nonzero() Function

Python NumPy nonzero() function is used to return the indices (the index numbers or index positions) of the elements of an array that are non-zero. It returns a tuple of arrays, one for each dimension of arr, containing the indices of the non-zero elements in that dimension. In this article, I will explain numpy.nonzero() function and use this syntax, parameters, and return indices of elements that are non-zero with examples.

1. Quick Examples of Python NumPy nonzero() Function

If you are in a hurry, below are some quick examples of how to use Python NumPy nonzero() function. For more creators of ndarray refer NumPy Tutorial.

# Below are the quick examples

# Example 1: Indices of non zero elements 
arr = np.array([8, 23, 45, 0, 60, 0, 85, 0, 101])
arr2 = np.nonzero(arr)

# Example 2: All nonzero elements
arr3 = arr[arr2]

# Example 3: Index of all elements which are greater than 50
arr2 = np.nonzero(arr > 50)

# Example 4: Use nonzero() function to 2-d array 
arr = np.array([[4, 0, 0], [0, 6, 0], [-7, 15, 0]])
arr2 = np.nonzero(arr)

# Example 5: Get the corresponding non-zero number                
arr3 = arr[np.nonzero(arr)]

# Example 6: Use numpy.transpose() to indices of non-zero number 
arr = np.array([[4, 0, 0], [0, 6, 0], [-7, 15, 0]])             
arr3 = np.transpose(np.nonzero(arr))

2. Syntax of Python numpy.nonzero()

Following is the syntax to create numpy.nonzero() function.

# Python numpy.nonzero() Syntax
numpy.nonzero(arr)

2.1 Parameters of NumPy nonzeros()

• arr : Input array.

2.2 Return Value of nonzeros()

It returns Indices of elements that are non-zero.

3. Get Indices of nonzero Elements Use nonzero()

We can use NumPy nonzero() function is used to get index of all elements which are non-zero.

import numpy as np

# Create one-dimensional array with nonzero
arr = np.array([8, 23, 45, 0, 60, 0, 85, 0, 101])

# Indices of non zero elements  
arr2 = np.nonzero(arr)
print (arr2) 

# Output:
# (array([0, 1, 2, 4, 6, 8], dtype=int64),)

# All nonzero elements
arr3 = arr[arr2]
print(arr3)

# Output:
# [  8  23  45  60  85 101]

# Index of all elements which are greater than 50
arr2 = np.nonzero(arr > 50)
print (arr2) 

# Output:
# (array([4, 6, 8], dtype=int64),)

4. Use nonzero() Function to 2-D Array

import numpy as np

# Create two-dimensional array with nonzero
arr = np.array([[4, 0, 0], [0, 6, 0], [-7, 15, 0]])

# Use nonzero() function to 2-d array 
arr2 = np.nonzero(arr)
print (arr2) 

# Output:
(array([0, 1, 2, 2], dtype=int64), array([0, 1, 0, 1], dtype=int64))

# Get the corresponding non-zero number                
arr3 = arr[np.nonzero(arr)]
print(arr3) 

# Output:
# [ 4  6 -7 15]

5. Use numpy.transpose() Function to Indices of non-zero Number

# Use numpy.transpose() function to indices of non-zero number 
arr = np.array([[4, 0, 0], [0, 6, 0], [-7, 15, 0]])             
arr3 = np.transpose(np.nonzero(arr))
print(arr3) 

# Output:
# [[0 0]
#  [1 1]
#  [2 0]
# [2 1]]

6. Conclusion

In this article, I have explained how to use Python NumPy nonzero() function using indices of elements that are non-zero with examples.

Happy Learning!!

Related Articles

• Get the cumulative sum of array
• Get the minimum value of NumPy array
• How to get square values of an array
• How to create NumPy one’s array
• Gets round values of NumPy array

References

• https://numpy.org/doc/stable/reference/generated/numpy.nonzero.html