How to Use np.squeeze in NumPy: Remove Single-Dimension Entries

Use np.squeeze to remove single-dimensional entries from the shape of a NumPy array. It simplifies arrays by eliminating axes with size 1, making data easier to work with.

Syntax

The basic syntax of np.squeeze is:

• np.squeeze(a, axis=None)

Where:

• a is the input array.
• axis is optional; it specifies which single-dimensional axes to remove. If None, all axes of size 1 are removed.

python

np.squeeze(a, axis=None)

Example

This example shows how np.squeeze removes single-dimensional entries from an array's shape.

python

import numpy as np

# Create a 3D array with shape (1, 3, 1)
a = np.array([[[1], [2], [3]]])
print('Original shape:', a.shape)

# Use np.squeeze to remove all single-dimensional axes
b = np.squeeze(a)
print('Squeezed shape:', b.shape)
print('Squeezed array:', b)

# Use np.squeeze with axis=0 to remove only the first axis
c = np.squeeze(a, axis=0)
print('Shape after squeezing axis 0:', c.shape)

# Trying to squeeze an axis that is not size 1 raises an error
try:
    np.squeeze(a, axis=1)
except ValueError as e:
    print('Error:', e)

Output

Original shape: (1, 3, 1)
Squeezed shape: (3,)
Squeezed array: [1 2 3]
Shape after squeezing axis 0: (3, 1)
Error: cannot select an axis to squeeze out which has size not equal to one

Common Pitfalls

Common mistakes when using np.squeeze include:

• Trying to squeeze an axis that is not size 1, which causes a ValueError.
• Not realizing that np.squeeze removes all size 1 axes by default, which may change the array shape more than expected.
• Using axis parameter incorrectly or with wrong axis indices.

Always check the array shape before and after squeezing to avoid unexpected results.

python

import numpy as np

arr = np.array([[1, 2, 3]])  # Shape (1, 3)

# Wrong: trying to squeeze axis 1 which is size 3
try:
    np.squeeze(arr, axis=1)
except ValueError as e:
    print('Wrong squeeze:', e)

# Right: squeeze axis 0 which is size 1
correct = np.squeeze(arr, axis=0)
print('Correct squeeze shape:', correct.shape)

Output

Wrong squeeze: cannot select an axis to squeeze out which has size not equal to one
Correct squeeze shape: (3,)

Quick Reference

np.squeeze Cheat Sheet:

Parameter	Description
a	Input array to squeeze
axis=None	Axes to remove if size 1; removes all if None

Returns: Array with single-dimensional entries removed.

Parameter	Description
a	Input array to squeeze
axis=None	Axes to remove if size 1; removes all if None

Key Takeaways

Use np.squeeze to remove axes of size 1 from a NumPy array's shape.

By default, np.squeeze removes all single-dimensional axes unless you specify the axis parameter.

Specifying an axis that is not size 1 causes a ValueError.

Check array shapes before and after squeezing to avoid unexpected shape changes.

np.squeeze helps simplify array dimensions for easier data processing.