Remove Every Nth Element From a NumPy Array

This tutorial will discuss about unique ways to remove every nth element from a numpy array.

Suppose we have a numpy array of numbers, like this,

numbers = np.array([34, 35, 78, 61, 56, 35, 90, 35])

We want to delete every 2nd element from this array.

For this we will create a boolean array or a mask, where every Nth element will be marked as False like this,

# Create a mask where each Nth element
# is marked as False
mask = np.arange(len(numbers)) % n != 0

mask = ~mask

It will return a boolean array where every Nth element is False. Then we can pass this modified boolean sequence into the subscript operator of number array like this,

# Remove every Nth element from the array
numbers = numbers[mask]

It will return a copy of number array after removing every Nth element from the original array.

In the below example we are going to remove every second element from the number array.

Let’s see the complete example,

import numpy as np

# create sample numpy array
numbers = np.array([34, 35, 78, 61, 56, 35, 90, 35])

print('Before removing elements:')
print(numbers)

# Nth value
n = 2

# Create a mask where each Nth element
# is marked as True
mask = np.arange(len(numbers)) % n != 0
mask = ~mask

# Remove every Nth element from the array
numbers = numbers[mask]

print('After removing elements:')
print(numbers)

Output

Before removing elements:
[34 35 78 61 56 35 90 35]
After removing elements:
[34 78 56 90]

Summary

We learned how to delete every Nth element from a NumPy Array in Python.