After using Arrays.sort() how do I reverse array to its initial position?

Question

I had to sort array to find its Median, but now I need to recover the initial value of array, put it as it was. Is that possible?

How about copy array before sort and after sort you can use your copy? — jker, Nov 27 '18 at 22:16
This. Any strategy for saving the original order and then sorting back to it would dwarf the time copying the array. — Duane, Nov 27 '18 at 22:19
@MartynasKrupskis Please mark one of the answers as accepted. — MC Emperor, Nov 12 '20 at 16:45

MC Emperor · Answer 1 · 2018-11-27T22:24:34.527

You can't do that. Sorting is irreversible. However, you could also add all elements of your original list to a new ArrayList and then sort that list.

List<String> original = ...;
List<String> copy = new ArrayList<>(original);
Collections.sort(copy);

I would not worry about the footprint of the copy. It is a shallow copy, that means that the elements themselves are not copied, but only a new list is created with references to the elements contained in the original list. And that operation is quite fast. I would only worry if the list was very, very big.

score 3 · Answer 2 · answered Nov 27 '18 at 22:21

3

Using @McEmperors answer but with arrays

Object[] saved = Arrays.copyOf(old, old.length);
Array.sort(old);

answered Nov 27 '18 at 22:21

Duane

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score 1 · Answer 3 · answered Nov 27 '18 at 22:24

There are several ways to achieve what you want:

copy the array before sorting

int[] unsorted = {2,3,1};
int[] sorted = unsorted.clone();
Arrays.sort(sorted);
//find mean in sorted then proceed with unsorted

create a custom sort function that retains a mapping between the positions.
find the mean without sorting

After using Arrays.sort() how do I reverse array to its initial position?

3 Answers3