The Numpy library in Python comes with a number of useful functions and methods to work with and manipulate the data in arrays. In this tutorial, we will look at how to get all the even elements from a Numpy array with the help of some examples.
Steps to get all the even values in Numpy array
You can use boolean indexing to filter the Numpy array such that the resulting array contains only the elements that specify a given condition. For example, values that are even.
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Step 1 – Create a Numpy array
First, we will create a Numpy array that we will be using throughout this tutorial.
import numpy as np # create a numpy array ar = np.array([1, 2, 3, 4, 5, 6, 7, 8]) # display the array print(ar)
[1 2 3 4 5 6 7 8]
Here, we used the
numpy.array() function to create a one-dimensional Numpy array containing some numbers.
Step 2 – Filter the array for even values using a boolean expression
To get all the even elements of a Numpy array, filter the array using boolean indexing.
Here, we will specify our boolean expression,
ar % 2 == 0 and then use the boolean array resulting from this expression to filter our original array. The
% (modulus) operator returns the remainder when the left value is divided by the right value. Since even numbers are divisible by 2,
ar % 2 will result in 0 if the number is even.
Let’s get all the even elements in the array created above
# even values in the array ar print(ar[ar % 2 == 0])
[2 4 6 8]
We get all the even values in the array
To understand what’s happening here, let’s look under the hood. Let’s see what we get from the expression
ar % 2 == 0.
ar % 2 == 0
array([False, True, False, True, False, True, False, True])
We get a Numpy array with boolean values. The values in this array represent whether a value at a particular index satisfies the given condition or not (if the value is even or not).
When we do
ar[ar % 2 == 0], we are essentially filtering the original array where the condition evaluates to
You can similarly filter a Numpy array for other conditions as well.
Summary – Get all even elements in a Numpy array
In this tutorial, we looked at how to get the even elements of a Numpy array. The following is a short summary of the steps mentioned –
- Create a Numpy array (skip this step if you already have an array to operate on).
- Use boolean indexing to filter the array for only the values that are even,
ar[ar % 2 == 0].
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