Beefy Boxes and Bandwidth Generously Provided by pair Networks
Perl-Sensitive Sunglasses

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.

Log In?

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://577610]
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others having an uproarious good time at the Monastery: (7)
As of 2016-10-23 10:53 GMT
Find Nodes?
    Voting Booth?
    How many different varieties (color, size, etc) of socks do you have in your sock drawer?

    Results (301 votes). Check out past polls.