I've used the same idiom, BrowserUK.

One minor nit, however - use a temp variable, and stringify the array before the grep. Stringifying @array2 for each element of @array1 is probably more expensive than building a hash.

Update: Unless I missed something on my benchmark, the faq is the fastest - by far! I didn't expect it, but I should have ;-)

I varied the size of the array and the faq consistently came out on top. The larger @array2 got, the better the faq performed.

#!/usr/bin/perl 
use strict;
use warnings;
use Benchmark qw/cmpthese/;
use vars qw/@array1 @array2/;

sub perlfaq { # lifted from nothingmuch's post above
    my %hash;
    $hash{$_} = undef foreach (@array2);
    @array1 = grep { not exists $hash{$_} } @array1;
}

sub buk { 
    grep{ local $"="\c1"; -1==index( "\c1@array2\c1", "\c1$_\c1") } @a
+rray1;
} 

sub improved {
    local $" = "\c1";
    my $temp = "\c1@array2\c1"; 
    grep { -1==index($temp, "\c1$_\c1") } @array1;
}

push @array1, int (rand 100) for (1 .. 1000);
push @array2, int (rand 100) for (1 .. 100);
cmpthese (1_000, {
    perlfaq => \&perlfaq,
    buk => \&buk,
    improved => \&improved,
})

__END__

Benchmark: timing 1000 iterations of buk, improved, perlfaq...
       buk: 58 wallclock secs (50.99 usr +  0.01 sys = 51.00 CPU) @ 19
+.61/s (n=1
000)
  improved:  4 wallclock secs ( 3.98 usr +  0.00 sys =  3.98 CPU) @ 25
+1.51/s (n=
1000)
   perlfaq:  1 wallclock secs ( 0.88 usr +  0.00 sys =  0.88 CPU) @ 11
+35.07/s (n
=1000)
           Rate      buk improved  perlfaq
buk      19.6/s       --     -92%     -98%
improved  252/s    1183%       --     -78%
perlfaq  1135/s    5689%     351%       --

[download]

In reply to Re: Re: subtract one array from another by jsprat
in thread subtract one array from another by Anonymous Monk

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