P.S. Using hashes will eliminate duplicate entries from both lists. My
assumption in suggesting this was that that wasn't a problem, but it is
something that should be made explicit.
Cheers,
Jeff
At 03:24 PM 6/8/01 -0700, Jeff Yoak wrote:
>Code to do what you are looking for is inserted into the loop below, with
>comments at the end.
>
>At 10:02 PM 6/8/01 +0000, scott lutz wrote:
>>I have a question that to me seems like it would be part of the
>>foundation of Perl.
>>
>>@possible_matches = qw( list of items to match against );
>>
>>
>>@list = qw( imagine that there is an unknown
>> number of elements in here );
>>
>>foreach $list (@list) {
>> # now match againt each value in @possible_matches, one-by-one,
>
> foreach my $item (@possible_matches) {
> if($list eq $item){
> # Do whatever you like, here, print it, store it,
> etc.
> }
> }
>
>>}
>
>As far as it being in part of the "fundamentals," the best thing I can
>suggest is that you consider using hashes. When you want to know if
>something is "in" a list, hashes leap naturally to mind.
>
>First you make the elements of your arrays above into keys of a hash. The
>values don't matter. If you don't also need them in arrays for some other
>purpose, you might do this directly with something like:
>
>my %possible_matches;
>@possible_matches{qw( list of items to match against )}=();
># This actually efficiently assigns to the hash with something called slicing.
># You'll find it in the standard books, including the llama on about page 73.
># (I don't have it here now.)
># The values, which you don't care about, will all be undef.
>my %list;
>@list{qw(item whatever baz bar)} = ();
>
>Now to get the same thing as above, you can ask more directly like this:
>
>foreach my $item (keys %possible_matches){
> if(exists $list{$item}){
> # do whatever
> }
>}
>
>or more succinctly:
>
>my @matches = grep {exists $list{$_}} keys %possible_matches;
>
>Enjoy!
>
>Cheers,
>Jeff
>
