How to shuffle two arrays to the same order

numpy, cookbook, python

This is a small recipe on how to get two arrays with the same shape (same length) shuffled with the same “random seed”. This is useful when the two arrays hold related data (for example, one holds values and the other one holds labels for those values).

It takes advantage of the fact that numpy arrays can be indexed with other arrays, something that seems really magical when compared to regular python arrays.

>>> import numpy as np
>>> x = np.arange(10)
>>> y = np.arange(9, -1, -1)
>>> x
array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])
>>> y
array([9, 8, 7, 6, 5, 4, 3, 2, 1, 0])
>>> s = np.arange(x.shape[0])
>>> np.random.shuffle(s)
>>> s
array([9, 3, 5, 2, 6, 0, 8, 1, 4, 7])
>>> x[s]
array([9, 3, 5, 2, 6, 0, 8, 1, 4, 7])
>>> y[s]
array([0, 6, 4, 7, 3, 9, 1, 8, 5, 2])