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?

Answer 1

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);

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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.

Answer 2

Using @McEmperors answer but with arrays

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

Answer 3

There are several ways to achieve what you want:

1. 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
   

2. create a custom sort function that retains a mapping between the positions.

3. find the mean without sorting