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Re: Getting the intersection of n collections.

by jdporter (Canon)
on Oct 11, 2006 at 14:17 UTC ( #577610=note: print w/ replies, xml ) Need Help??

in reply to Getting the intersection of n collections.

I point out that solutions which perform set unions pair-wise, iteratively on the set of lists do not scale well. Consider the worst-case scenario, where all of the lists are identical, and there's a million of them.

A better approach is the counting one, like that suggested by dtr, but uniqifying each list by converting it to its corresponding set hash, as basje did.

my %counts; for my $ar ( @arrays ) { my %set; @set{ @$ar } = (); # this is faster. $counts{$_}++ for keys %set; } my @union = grep { $counts{$_} == @arrays } keys %counts;
We're building the house of the future together.

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