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How to add dimension to Numpy array?

Posted on April 7, 2021March 2, 2023 By Luke K

Let’s check how to add a dimension to a Numpy array. We will use the newaxis and expand_dims functions.
Numpy ways to expand arrays Python

In this Python tutorial, I’ll show a few ways to expand the Numpy array by adding another dimension.

Let’s start with the easiest way.

Adding dimension with the newaxis method

import numpy as np

my_array = np.arange(6).reshape(3, 2)
print(f"My array shape is: \n {my_array.shape}")

my_expanded_array = my_array[:, np.newaxis, :, np.newaxis]
print(f"My expanded array shape is: \n {my_expanded_array.shape}")

I am using the newaxis function and adding it as a parameter exactly where I can add a new axis.

My array shape is: 
 (3, 2)
My expanded array shape is: 
 (3, 1, 2, 1)

This is how to add dimensions at the beginning of the Numpy array.

import numpy as np

my_array = np.arange(6).reshape(3, 2)
print(f"My array shape is: \n {my_array.shape}")

my_expanded_array = my_array[:, np.newaxis, :, np.newaxis]
print(f"My expanded array shape is: \n {my_expanded_array.shape}")

my_another_array = my_array[:, :, np.newaxis, np.newaxis]
print(f"My another expanded array shape is: \n {my_another_array.shape}")

Thanks to my_array[:, :, np.newaxis, np.newaxis] it is placed at the beginning of the array.

My array shape is: 
 (3, 2)
My expanded array shape is: 
 (3, 1, 2, 1)
My another expanded array shape is: 
 (3, 2, 1, 1)

Adding dimension with the expand_dims method

There is also the expand_dims Numpy function when newaxis is not enough for you.

See also  How to save array as csv file with Numpy?

The easiest example is to tell Numpy where to add a dimension to an array as a parameter.

import numpy as np

my_array = np.arange(6).reshape(3, 2)
print(f"My array shape is: \n {my_array.shape}")

my_expand_dims_array = np.expand_dims(my_array, axis=2)
print(f"My expand dims array shape is: \n {my_expand_dims_array.shape}")

I wrote np.expand_dims(my_array, axis=2) to add the axis as a third dimension.

My array shape is: 
 (3, 2)
My expand dims array shape is: 
 (3, 2, 1)

There is also the possibility to add multiple axes with expand_dims. To add multiple dimensions to a Numpy array, just use tuple values as the expand_dims parameter.

import numpy as np

my_array = np.arange(6).reshape(3, 2)
print(f"My array shape is: \n {my_array.shape}")

my_expand_dims_array = np.expand_dims(my_array, axis=2)
print(f"My expand dims array shape is: \n {my_expand_dims_array.shape}")

my_expand_dims_array = np.expand_dims(my_array, axis=(0, 1, 4))
print(f"My expand dims array shape is: \n {my_expand_dims_array.shape}")

I used np.expand_dims (my_array, axis= (0, 1, 4) to add the first, second, and fifth axes.

My array shape is: 
 (3, 2)
My expand dims array shape is: 
 (3, 2, 1)
My expand dims array shape is: 
 (1, 1, 3, 2, 1)

For sure, you know now how to add dimensions to Numpy arrays.

See also  Swap Numpy row vector to column vector
numpy Tags:array, axis, dimension

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