How to Use Negative Indexing in NumPy Arrays

In NumPy, you can use negative indexing to access elements from the end of an array by using negative numbers like -1 for the last element, -2 for the second last, and so on. This works similarly to Python lists and helps quickly select elements counting backward.

Syntax

Negative indexing in NumPy uses a negative integer inside square brackets to select elements from the end of an array.

• array[-1]: selects the last element
• array[-2]: selects the second last element
• array[-n]: selects the nth element from the end

python

element = array[-1]

Example

This example shows how to create a NumPy array and access elements using negative indexing to get the last and second last values.

python

import numpy as np

array = np.array([10, 20, 30, 40, 50])
last_element = array[-1]
second_last_element = array[-2]

print(f"Last element: {last_element}")
print(f"Second last element: {second_last_element}")

Output

Last element: 50
Second last element: 40

Common Pitfalls

One common mistake is using a negative index that is out of range, which causes an IndexError. For example, if the array length is 5, using -6 will fail.

Also, negative indexing works element-wise, but when slicing, be careful with start and stop positions as negative indices count from the end.

python

import numpy as np

array = np.array([1, 2, 3, 4, 5])

# Wrong: IndexError because -6 is out of range
# print(array[-6])

# Right: Use valid negative index
print(array[-5])  # prints 1

# Slicing with negative indices
print(array[-3:])  # prints last 3 elements [3 4 5]

Output

1
[3 4 5]

Quick Reference

Negative Index	Meaning	Example with array [10, 20, 30, 40, 50]
-1	Last element	50
-2	Second last element	40
-3	Third last element	30
-len(array)	First element	10

Key Takeaways

Negative indexing in NumPy accesses elements from the end using negative numbers.

Use -1 for the last element, -2 for the second last, and so on.

Negative indices must be within the array length to avoid errors.

Negative indexing works with slicing but be careful with start and stop positions.

It is a quick way to access elements without calculating positive indices.