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

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!