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Python NumPy For Your Grandma | Section 3.2 | newaxis

December 29, 2019
python courses

This video covers the newaxis keyword for inserting a new axis into a numpy array to increase its dimensionality. newaxis is usually used to make arrays compatible for broadcasting.


import numpy as np

# make 1d arrays
A = np.array([3, 11, 4, 5])
B = np.array([5, 0, 3])

# Deduct each element of B from each element of A
A[np.newaxis, :] - B[:, np.newaxis]

# Same as above, using None
A[None, :] - B[:, None]


Sometimes you may want to increase the dimensionality of an array by giving it a new axis. For example, suppose you have the following 1d arrays.
If you wanted to deduct each element of B from each element of A, you’d need to make the arrays compatible for subtraction. If A was a 1x4 array and B was a 3x1 array, A minus B would broadcast to your desired result. Surprise: you can use np.newaxis to promote the dimensionality of A and B for tasks like these. To use it, just put np.newaxis in the square bracket notation where ever you want to add a new axis.
For example, “A square bracket new axis comma colon” inserts a new axis in front of A’s existing axis, turning A into a 1x4 array and “B colon comma new axis” inserts a new axis behind B’s existing axis, turning B into a 3x1 array.
Note that newaxis is just an alias for the keyword None, so you’ll often see people using the None keyword here.

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