[python] Better way to shuffle two numpy arrays in unison

Shuffle any number of arrays together, in-place, using only NumPy.

import numpy as np


def shuffle_arrays(arrays, set_seed=-1):
    """Shuffles arrays in-place, in the same order, along axis=0

    Parameters:
    -----------
    arrays : List of NumPy arrays.
    set_seed : Seed value if int >= 0, else seed is random.
    """
    assert all(len(arr) == len(arrays[0]) for arr in arrays)
    seed = np.random.randint(0, 2**(32 - 1) - 1) if set_seed < 0 else set_seed

    for arr in arrays:
        rstate = np.random.RandomState(seed)
        rstate.shuffle(arr)

And can be used like this

a = np.array([1, 2, 3, 4, 5])
b = np.array([10,20,30,40,50])
c = np.array([[1,10,11], [2,20,22], [3,30,33], [4,40,44], [5,50,55]])

shuffle_arrays([a, b, c])

A few things to note:

  • The assert ensures that all input arrays have the same length along their first dimension.
  • Arrays shuffled in-place by their first dimension - nothing returned.
  • Random seed within positive int32 range.
  • If a repeatable shuffle is needed, seed value can be set.

After the shuffle, the data can be split using np.split or referenced using slices - depending on the application.

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