Re: array comparison question

Assuming the arrays are called @a1, @a2, @a3, the following ought to work (although I didn't test it). It should work correctly even if a value appears twice in a single array. This technique is trivially adaptable for different number of arrays, or different counts.

my @twice = do {
    my %a;
    map {my $a = $_; map {$a{$_}{$a}++} @$a} \@a1, \@a2, \@a3;
    grep {2 == keys %{$a{$_}}} keys %a;
};
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Re^2: array comparison question by reasonablekeith (Deacon) on Aug 23, 2005 at 15:58 UTC
it's a good solution, but I hate to see 'map' used instead of a 'for' unnecessarily, why make perl go to the trouble of building a return array if you're just going to ignore it? . `my @twice = do { my %tracker; foreach my $a_ref (\@a1, \@a2, \@a3) { foreach my $a_value (@$a_ref) { $tracker{$a_value}{$a_ref} = undef; } } grep {2 == keys %{$tracker{$_}}} keys %tracker; };` [download] --- my name's not Keith, and I'm not reasonable.	[reply] [d/l]
Re^3: array comparison question by Fletch (Bishop) on Aug 23, 2005 at 16:49 UTC
So long as you're using 5.8.1 or newer `map` in a void context won't build a return list. See `perldoc perl581delta` in the section "Miscellaneous Enhancements". (Having said that, stylistically I'm with you. :) -- We're looking for people in ATL	[reply] [d/l] [select]