On Aug 10, Jennifer Pan said:
>I have two list,
>@list1 and @list2, each element @list1 is unique (could be a hash I
>suppose)
>
>I want to find out all the elements @list2 that is an element in list1
>and have appeared two or more times
>
>I want to use GREP but I don't know how to grep certain element only
>when it happens >2 times, or is it possible?
>
>foreach $L1 (@list1) {
> if ( grep /$L1/ @list2 more than twice?) {
> print $L1;
>}
grep() returns the elements that passed in list context, and the NUMBER of
elements that passed in scalar context.
for $element (@list1) {
if (grep($_ eq $element, @list2) > 1) { print $element }
}
But I don't like the looks of that, really. We're going through the array
a lot.
I'd do something like:
my %freq;
$freq{$_}++ for @list2; # create a hash of key -> frequency
for (@list1) {
print $freq{$_} if $freq{$_} > 1;
}
This only loops through each array once. Your way loops through @list2
many times.
--
Jeff "japhy" Pinyan [EMAIL PROTECTED] http://www.pobox.com/~japhy/
RPI Acacia brother #734 http://www.perlmonks.org/ http://www.cpan.org/
** Look for "Regular Expressions in Perl" published by Manning, in 2002 **
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