🔒 Array shuffling mapping

[small siren]

I have a question regarding two arrays with 1 a shuffled version of the other. My question is how do we return the shuffled array back to the original array?

[zinc cosmos]

@small siren

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[small siren]

For Example:

arr1 = np.array([[1, 2, 3],
                 [4, 5, 6],
                 [7, 8, 9]])


arr2 = np.array([[4, 5, 6],
                 [7, 8, 9],
                 [1, 2, 3]])

I want to reset arr2 back to arr1 based on the indices on arr1

[finite cliff]

import random

a = [1, 2, 3,4 , 5]
b = somehow_shuffle(a)
a[:] = b

you can also shuffle "in place" with random.shuffle

ah, those are numpy arrays. My idea might work, or it might not; I don't use numpy

[small siren]

im not talking about how to shuffle, i'm talking about how to return the suffled array back to the original array

[static fulcrum]

It would be easier if you shuffled the indices and not the arrays themselves

[finite cliff]

see above under a[:] = b

might not work, but it shouldn't take long to try it

[static fulcrum]

E.g. you had this instead

arr = np.array(...)
indices = np.random.shuffle(np.arange(arr.shape[0]))
shuffled_arr = arr[indices]

[small siren]

im trying to convert arr2 back to arr1

[static fulcrum]

Your snippet doesn't make much sense right now, because instead of somehow "converting" arr2 back to arr1, you could just set arr2 = arr1.copy() and it would achieve the same thing

[small siren]

arr2 is a shuffled version based on arr1 by shuffling the rows, what I want is a general method to resort the shuffled rows from arr2 back to arr1

based on the row indices

[static fulcrum]

What I mean is, the end result of "resorting" arr2 is just arr1; Thus just copying would achieve the same thing

[small siren]

i want to find the index mapping to reshuffle it back

[static fulcrum]

So do you mean that in addition to

arr1 = np.array([[1, 2, 3],
                 [4, 5, 6],
                 [7, 8, 9]])


arr2 = np.array([[4, 5, 6],
                 [7, 8, 9],
                 [1, 2, 3]])
```You also have this
```py
shuffled_indices = [2, 1, 0]
```And you want to use `shuffled_indices` to transform `arr2` back?

[small siren]

yes

i think its supposed to be [1, 2, 0]

[static fulcrum]

No, shuffled_indices is how you get from arr1 to arr2
So what you actually mean is you want to calculate [1, 2, 0] from an original array arr1 and a shuffled array arr2

One problem is that there might be multiple solutions (think duplicate elements)

[small siren]

my problem there wont be duplicates

[static fulcrum]

I think this answers your question

[zinc cosmos]

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