Actually, is there a good reason why the builtin sort compare doesn't compare references to arrays in this fashion?

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@/=map{[/./g]}qw/.h_nJ Xapou cets krht ele_ r_ra/;
map{y/X_/\n /;print}map{pop@$_}@/for@/
[download]

s/2%/50%/ (roughly, depending). And it isn't just the comparison routine that is the problem. Constructing a huge number of tiny arrays takes some time (and memory).

I think fast, flexible, stable sort can be rolled into a module that makes the key construction easy and natural where the module overhead is low and outside of the sorting and so using the module would give performance (in speed and memory use) on par with a very efficient hand-rolled solution and much faster than any general-purpose Perl sorting modules I've looked at.

Having sort default to sorting array references as you've specified certainly makes sense. The boring answer is that backward compatibility prevents it from happening in Perl5. I won't pretend to remember how this type of operation is likely to behave in Perl6.

- tye        

Okay, fair enough - the allocation of all those arrays would probably hurt severely. Much better to do the sort-the-indexes trick you mention elsewhere in this thread, or the GRT variant mentioned in fast, flexible, stable sort.

But as for backwards compatibility - are you sure? Isn't the sorting of array references at this point essentially a random shuffle? (Meaning that it is unspecified, and could be different each time you run perl, not that it can be used in a situation where you actually need a random shuffle) Couldn't some order therefore be imposed upon it?

--
@/=map{[/./g]}qw/.h_nJ Xapou cets krht ele_ r_ra/;
map{y/X_/\n /;print}map{pop@$_}@/for@/
[download]

If sort {$a<=>$b} is indeed optimized (it seems so), you can just use it for a floating-point key, you just have to 'no warnings "numeric"; and put the float in the first place.

You are, however, right in that if the key is more complicated, this method is not applicable. (You can however gain with the ST only if calculating the key is much slower than comparing them.)