How to Count Occurrences of Elements in NumPy


You can use the following methods to count the occurrences of elements in a NumPy array:

Method 1: Count Occurrences of a Specific Value

np.count_nonzero(x == 2)

Method 2: Count Occurrences of Values that Meet One Condition

np.count_nonzero(x < 6)

Method 3: Count Occurrences of Values that Meet One of Several Conditions

np.count_nonzero((x == 2) | (x == 7))

The following examples show how to use each method in practice with the following NumPy array:

import numpy as np

#create NumPy array
x = np.array([2, 2, 2, 4, 5, 5, 5, 7, 8, 8, 10, 12])

Example 1: Count Occurrences of a Specific Value

The following code shows how to count the number of elements in the NumPy array that are equal to the value 2:

#count number of values in array equal to 2
np.count_nonzero(x == 2)

3

From the output we can see that 3 values in the NumPy array are equal to 2.

Example 2: Count Occurrences of Values that Meet One Condition

The following code shows how to count the number of elements in the NumPy array that have a value less than 6:

#count number of values in array that are less than 6
np.count_nonzero(x < 6)

7

From the output we can see that 7 values in the NumPy array have a value less than 6.

Example 3: Count Occurrences of Values that Meet One of Several Conditions

The following code shows how to count the number of elements in the NumPy array that are equal to 2 or 7:

#count number of values in array that are equal to 2 or 7
np.count_nonzero((x == 2) | (x == 7))

4

From the output we can see that 4 values in the NumPy array are equal to 2 or 7.

Additional Resources

The following tutorials explain how to perform other common operations in Python:

How to Calculate the Mode of NumPy Array
How to Map a Function Over a NumPy Array
How to Sort a NumPy Array by Column

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