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From: merlyn@iwarp.intel.com (Randal Schwartz)
Newsgroups: comp.lang.perl
Subject: Re: Best way to nullify an intersection
Message-ID: <1990Jul3.170621.28795@iwarp.intel.com>
Date: 3 Jul 90 17:06:21 GMT
References: <601@inpnms.ROCKVILLE.DG.COM>
Sender: news@iwarp.intel.com
Reply-To: merlyn@iwarp.intel.com (Randal Schwartz)
Organization: Stonehenge; netaccess via Intel, Beaverton, Oregon, USA
Lines: 48
In-Reply-To: logan@rockville.dg.com (James L. Logan)

In article <601@inpnms.ROCKVILLE.DG.COM>, logan@rockville (James L. Logan) writes:
| Is there a better or faster way to drop all elements in set B that
| intersect with set A?  Here's what I've got so far:
| 
| 	open(FILE1, "file1") || die;
| 	@A = <FILE1>;
| 	close(FILE1) || die;
| 
| 	open(FILE2, "file2") || die;
| 	@B = <FILE2>;
| 	close(FILE2) || die;
| 
| 	foreach $element (@A) {
| 		foreach (@B) {
| 			if (/^$element$/) {
| 				$_ = '';
| 				last;
| 			}
| 		}
| 	}
| 	print @B;
| 
| Also, how can I delete the element that was matched in @B, while
| also shortening the array by one element; rather than just
| setting the element to the null string?  

Well, I'd attack it something like this:

open(F1,"file1") || die "cannot open file1: $!";
while (<F1>) {
	$saw{"$_"}++;
}
close(F1);

open(F2,"file2") || die "cannot open file2: $!";
while (<F2>) {
	print unless $saw{$_};
}
close(F2);

Using the keys of an assoc array as a set-type is a very handy idiom.

print "Just another Perl hacker,"
-- 
/=Randal L. Schwartz, Stonehenge Consulting Services (503)777-0095 ==========\
| on contract to Intel's iWarp project, Beaverton, Oregon, USA, Sol III      |
| merlyn@iwarp.intel.com ...!any-MX-mailer-like-uunet!iwarp.intel.com!merlyn |
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