I need sorting VI that returns the sorted array element's positions in the unsorted array

Question

I need a VI that will very quickly (n log n) sort a 1D array of doubles.  This VI should not only output the sorted array, but for each of the sorted array elements, it should also output that sorted array element's position in the unsorted array.  So for example if the input array were:
unsorted_array
4.1
2.3
7.0
5.6
10.2
Then the output arrays would be:
sorted_array
2.3
4.1
5.6
7.0
10.2
indices_array
1 (the value 2.3 is located at position 1 in the unsorted_array)
0 (the value 4.1 is located at position 0 in the unsorted_array)
3 (the value 5.6 is located at position 3 in the unsorted_array)
2 (the value 7.0 is located at position 2 in the unsorted_array)
4 (the value 10.2 is located at position 4 in the unsorted_array)
This way I could generate the sorted_array using just the indices_array and the unsorted_array.  Has anyone written a nifty piece of code to do this?  I did some research on (n log n) sorting algorithms but most of them use recursion which I don't know how to do in LabVIEW.  It would also be nice to have an algorithm like this that could sort an array of strings.
cheers,
Richard

Answer 1

Try something like the attached example (LabVIEW 7.0). I think it does what you need.
(To understand the code, it is important to know that arrays of clusters are sorted by the first element in the cluster).
Sort array itself sorts also array of strings, so you could just substitute, keeping the rest of the code the same.
Sort array uses a variation of quicksort, so it should have about NlogN complexity.
(If you think you only need the array of indices to later generate the sorted array, it does not make much sense to even do it. To get the indices, you need to sort the array anyway. You should just sort the plain array directly.
Message Edited by altenbach on 07-13-2005 03:47 PM
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Attachments:
SortAndIndex.vi ‏26 KB