Ruby's sort algorithm is quicksort, last I checked, and quicksort is not stable (which is the property you're looking for in a sort). �There are a bunch of ways around this, including writing your own, but one cute, quick, but possibly performance-impairing, approach I've seen (Matz's suggestion) is:

Apparently it's also possible in 1.9.x (and thus MacRuby) to do:

��ary.sort_by.with_index {|x, i| [x, i]}

It's not much faster, though. �In the end, I'd probably suggest writing your own, if the performance of this is too poor. �(One person claimed this was on the order of 50 times slower; I haven't benchmarked it myself.) �Mergesort is stable, for example.

This is a common problem; most systems don't need a stable sort, so they use Quicksort as a 'best general purpose' algorithm.

-- �Morgan

On Sun, Jan 30, 2011 at 12:03 PM, Robert Rice <rice.audio@pobox.com> wrote:

Hi:

Does the Ruby Array sort algorithm maintain the relative position for children returning the same value for the comparison? I had an instance where two children having the compare value were interchanged.

Thanks,
Bob Rice

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