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I'm trying to sort the rows of one array by the values of another. For example:

import numpy as np
arr1 = np.random.normal(1, 1, 80)
arr2 = np.random.normal(1,1, (80,100))

I want to sort arr1 in descending order, and to have the current relationship between arr1 and arr2 to be maintained (ie, after sorting both, the row of arr1[0] and arr2[0, :] are the same).

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2 Answers

up vote 4 down vote accepted

Use argsort:

arr1inds = arr1.argsort()
sorted_arr1 = arr1[arr1inds[::-1]]
sorted_arr2 = arr2[arr1inds[::-1]]

EDIT: changed to descending order

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Thanks for the tip! – mike Jan 25 '12 at 18:50
up vote 0 down vote

Use the zip function: zip( *sorted( zip(arr1, arr2) ) ) This will do what you need.

Now the explanation: zip(arr1, arr2) will combine the two lists, so you've got [(0, [...list 0...]), (1, [...list 1...]), ...] Next we run sorted(...), which by default sorts based on the first field in the tuple. Then we run zip(...) again, which takes the tuples from sorted, and creates two lists, from the first element in the tuple (from arr1) and the second element (from arr2).

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