ordering an array based on values of another array

Question

This question is probably basic for some of you but it I am new to Python. I have an initial array:

initial_array = np.array ([1, 6, 3, 4])

I have another array.

value_array= np.array ([10, 2, 3, 15])

I want an array called output array which looks at the values in value_array and reorder the initial array.

My result should look like this:

output_array = np.array ([4, 1, 3, 6])

Does anyone know if this is possible to do in Python?

So far I have tried:

for i in range(4):
      find position of element

Mahdi F. · Accepted Answer · 2022-12-06 20:46:15Z

2

You can use numpy.argsort to find sort_index from value_array then rearrange the initial_array base sort_index in the reversing order with [::-1].

>>> idx_sort = value_array.argsort()
>>> initial_array[idx_sort[::-1]]
array([4, 1, 3, 6])

answered Dec 6, 2022 at 20:46

Mahdi F.

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bracko · Accepted Answer · 2022-12-06 20:56:23Z

1

You could use stack to put arrays together - basically adding column to initial array, then sort by that column.

import numpy as np

initial_array =  np.array ([1, 6, 3, 4])

value_array =  np.array ([10, 2, 3, 15])

output_array = np.stack((initial_array, value_array), axis=1)

output_array=output_array[output_array[:, 1].argsort()][::-1]
print (output_array)

[::-1] part is for descending order. Remove to get ascending. I am assuming initial_array and values_array will have same length.

answered Dec 6, 2022 at 20:56

bracko

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