Wednesday, April 2, 2008


Frequently I confront the situation that I need to compare two array or two hash keys. When I was in the way, I just compared each element of an array to another using 'for statement' .

@array1=qw / a b c d e /;
@array2=qw / a b d e f /;

for $i ( @array1 ){
for $j ( @array2 ){
push @common, $i if $i eq $j ;

The above conventional code could be reduced as below using List::Compare

$lc = List::Compare->new(\@array1, \@array2);

@intersection = $lc->get_intersection;
@union = $lc->get_union;

List::Compare find a set of common array element by using hash referencing one of array.
The same algorithm List::Compare used could be like below

my %hash_1;
my @common;
$hash_1{$_}++ for @array1;
@common=map{ $hash_1{$_}?$_:()} @array2;

According to my benchmark test, for comparing two arrays size of 10,000, List::Compare took 0.28 sec, hash reference took 0.04 sec and conventional double for statement took 26.93 sec.