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Re: Compare arrays remove identical

by perlmonkey (Hermit)
on May 02, 2001 at 11:26 UTC ( #77256=note: print w/ replies, xml ) Need Help??

in reply to Compare arrays remove identical

Theres a section in Mastering Algorithms with Perl on sets also. If you need a full implementation of unions/differences/intersections etc see the Set::Scalar module. If you use chromatic's code linked to above, I gave into my compulsion to do a tiny bit of benchmarking:

my @kansas = qw( corn wheat hay cattle ); my @oklahoma = qw( wheat dairy cattle ); use Benchmark; timethese(100000, { "diff1" => sub { diff1(\@kansas, \@oklahoma) }, "diff2" => sub { diff2(\@kansas, \@oklahoma) }, }); sub diff1 { my %hash; @hash{@{$_[1]}} = (1) x @{$_[1]}; return grep { !defined $hash{$_} } @{$_[0]}; } sub diff2 { my %hash = map{ $_=>1} @{$_[1]}; return grep { !defined $hash{$_} } @{$_[0]}; }
It seems that a hash slice is a teeny bit faster than map for this purpose:
Benchmark: timing 100000 iterations of diff1, diff2... diff1: 2 wallclock secs ( 1.74 usr + 0.01 sys = 1.75 CPU) diff2: 3 wallclock secs ( 2.22 usr + 0.01 sys = 2.23 CPU)

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