How to sort a list with duplicates and return their unique indices.

[deanhystad]

I think DeaD_EyE is not interpreting the question correctly. I do not think "unique" means that the lst should be pared down to only contain unique values. I think the problem is the way the index sort was done returned non-unique values. The problem is caused by using "index" which returns the first match, not the index of the element.

To solve the problem, create a list of index values, and sort these using a key that references the original list. This is what perfingo did with the index, value tuples. Another way to do the same thing is create a separate list of index values and sort the index list using a key that references the original list.

lst = [48,52,35,35,44,35]
index = range(len(lst))
sorted_index = sorted(index, key=lambda i: lst[i])
print(sorted_index)

I like perfingo's method because it produces the sorted list and the sorted index list at the same time. I would use that if I needed both results. If I only needed the sorted index list I might use the separate array.

You could also do this with numpy's argsort()

import numpy as np

lst = np.array([48,52,35,35,44,35])
print(lst.argsort())