# Better way to shuffle two numpy arrays in unison

| | | | | | | | | | | | | | | | | | | |

I have two numpy arrays of different shapes, but with the same length (leading dimension). I want to shuffle each of them, such that corresponding elements continue to correspond -- i.e. shuffle them in unison with respect to their leading indices.

This code works, and illustrates my goals:

``````def shuffle_in_unison(a, b):
assert len(a) == len(b)
shuffled_a = numpy.empty(a.shape, dtype=a.dtype)
shuffled_b = numpy.empty(b.shape, dtype=b.dtype)
permutation = numpy.random.permutation(len(a))
for old_index, new_index in enumerate(permutation):
shuffled_a[new_index] = a[old_index]
shuffled_b[new_index] = b[old_index]
return shuffled_a, shuffled_b
``````

For example:

``````>>> a = numpy.asarray([[1, 1], [2, 2], [3, 3]])
>>> b = numpy.asarray([1, 2, 3])
>>> shuffle_in_unison(a, b)
(array([[2, 2],
[1, 1],
[3, 3]]), array([2, 1, 3]))
``````

However, this feels clunky, inefficient, and slow, and it requires making a copy of the arrays -- I"d rather shuffle them in-place, since they"ll be quite large.

Is there a better way to go about this? Faster execution and lower memory usage are my primary goals, but elegant code would be nice, too.

``````def shuffle_in_unison_scary(a, b):
rng_state = numpy.random.get_state()
numpy.random.shuffle(a)
numpy.random.set_state(rng_state)
numpy.random.shuffle(b)
``````

This works...but it"s a little scary, as I see little guarantee it"ll continue to work -- it doesn"t look like the sort of thing that"s guaranteed to survive across numpy version, for example.

## Shop

Best Python online courses for 2022

\$FREE

Best laptop for Excel

\$

Best laptop for Solidworks

\$399+

Best laptop for Roblox

\$399+

Best computer for crypto mining

\$499+

Best laptop for Sims 4

\$

Best laptop for Zoom

\$499

Best laptop for Minecraft

\$590

Latest questions

PythonStackOverflow

Common xlabel/ylabel for matplotlib subplots

PythonStackOverflow

Check if one list is a subset of another in Python

PythonStackOverflow

How to specify multiple return types using type-hints

PythonStackOverflow

Printing words vertically in Python

PythonStackOverflow

Python Extract words from a given string

PythonStackOverflow

Why do I get "Pickle - EOFError: Ran out of input" reading an empty file?

PythonStackOverflow

Python os.path.join () method

PythonStackOverflow

Flake8: Ignore specific warning for entire file

## Wiki

Python | How to copy data from one Excel sheet to another

Common xlabel/ylabel for matplotlib subplots

Check if one list is a subset of another in Python

How to specify multiple return types using type-hints

Printing words vertically in Python

Python Extract words from a given string

Cyclic redundancy check in Python

Finding mean, median, mode in Python without libraries