You can use the following methods to filter the values in a NumPy array:
Method 1: Filter Values Based on One Condition
#filter for values less than 5
my_array[my_array 5]
Method 2: Filter Values Using “OR” Condition
#filter for values less than 5 or greater than 9 my_array[(my_array 5) | (my_array > 9)]
Method 3: Filter Values Using “AND” Condition
#filter for values greater than 5 and less than 9 my_array[(my_array > 5) & (my_array 9)]
Method 4: Filter Values Contained in List
#filter for values that are equal to 2, 3, 5, or 12 my_array[np.in1d(my_array, [2, 3, 5, 12])]
This tutorial explains how to use each method in practice with the following NumPy array:
import numpy as np
#create NumPy array
my_array = np.array([1, 2, 2, 3, 5, 6, 7, 10, 12, 14])
#view NumPy array
my_array
array([ 1, 2, 2, 3, 5, 6, 7, 10, 12, 14])
Example 1: Filter Values Based on One Condition
The following code shows how to filter values in the NumPy array based on just one condition:
#filter for values less than 5 my_array[(my_array 5)] array([1, 2, 2, 3]) #filter for values greater than 5 my_array[(my_array > 5)] array([ 6, 7, 10, 12, 14]) #filter for values equal to 5 my_array[(my_array == 5)] array([5])
Example 2: Filter Values Using “OR” Condition
The following code shows how to filter values in the NumPy array using an “OR” condition:
#filter for values less than 5 or greater than 9 my_array[(my_array 5) | (my_array > 9)] array([ 1, 2, 2, 3, 10, 12, 14])
This filter returns the values in the NumPy array that are less than 5 or greater than 9.
Example 3: Filter Values Using “AND” Condition
The following code shows how to filter values in the NumPy array using an “AND” condition:
#filter for values greater than 5 and less than 9 my_array[(my_array > 5) & (my_array 9)] array([6, 7])
This filter returns the values in the NumPy array that are greater than 5 and less than 9.
Example 4: Filter Values Contained in List
The following code shows how to filter values in the NumPy array that are contained in a list:
#filter for values that are equal to 2, 3, 5, or 12 my_array[np.in1d(my_array, [2, 3, 5, 12])] array([ 2, 2, 3, 5, 12])
This filter returns only the values that are equal to 2, 3, 5, or 12.
Note: You can find the complete documentation for the NumPy in1d() function here.
Additional Resources
The following tutorials explain how to perform other common filtering operations in Python:
How to Filter Pandas DataFrame Rows that Contain a Specific String
How to Filter a Pandas DataFrame on Multiple Conditions
How to Use “NOT IN” Filter in Pandas DataFrame