Hello, I have two snippets of code which get the intersection of two hash arrays and am wondering about performance on large scale data.

In a nutshell, what kind of performance is to be expected using grep vs looping through hashes? looking at the grep source code, it has a lot of buffering, I've tried to find some details on internals of memory allocation of hashes but ???

I read this "This does mean that hashes eat up a I<lot> of memory, both in memory Devel::Size can track (the memory actually in the structures and strings) and that it can't (the malloc alignment and length overhead)." from here http://cpansearch.perl.org/src/TELS/Devel-Size-0.71/lib/Devel/Size.pm

or perhaps is it possible to unroll the loop and thread it?

my %inter;
for (keys %hist1)
{
    if (exists $hist2{$_})
    {
        my $val1 = $hist1{$_};
        my $val2 = $hist2{$_};
        $inter{$_} = ($val1 <= $val2) ? $val1 : $val2;
    }
}

[download]
my @common = grep exists $hist1{$_}, sort keys %hist2;

[download]

Thanks for any insight.

In reply to memory:: grep vs looping through hash by f77coder

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