Incredible trick on how to reshape to automatic value of dimension in Numpy

Let’s learn how to reshape to automatic value of dimension in Numpy Python library.

Why you need the trick

You may need this trick when:

you don’t know the size of the base array

you expect base array to change size

you don’t know which value of dimension to put

The trick is:

put -1 as a value!

How to do the trick

See the example code:

import numpy as np
my_array = np.random.random([6, 6])
print(f'The original array: \n {my_array}')

reshaped_array = my_array.reshape(2, -1, 3)
print(f'The modified array: \n {reshaped_array}')

As you can see I put reshape(2, -1, 3) and it worked. Numpy automatically guessed that it should be 6 instead of -1.

Remember: you can use -1 only once!

When to use the trick

You can use the `-1` value to automatically resize Numpy arrays in the following cases:

When you don’t know the size of the base array.
When you expect the base array to change size.
When you don’t know which value of dimension to put.