On Jan 29, Jason Purdy said:
>my ( @filea, @fileb, @inAButNotInB, @inBButNotInA );
I don't see any hashes being used. This feels like it's going to be very
inefficient.
>open ( FILEA, shift ) || die "Cannot open 1st file: $!\n";
>@filea = <FILEA>;
>close ( FILEA );
>
>open ( FILEB, shift ) || die "Cannot open 2nd file: $!\n";
>@fileb = <FILEB>;
>close ( FILEB );
>
>foreach my $object ( @filea ) {
> chomp $object;
> push @inAButNotInB, $object if ( !grep(/$object/, @fileb) );
And indeed it is. Do not use grep(/$foo/, LIST) to determine if $foo is
in LIST, for a myriad of reasons. First, you're using a regex, so if $foo
has any regex metacharacters in it, you'll get false negatives and false
positives. Second, you're not anchoring the regex at all, so if LIST
contains "rabbit" and $foo is "bit", you'll get a false positive. Third,
grep() goes through the ENTIRE list. Imagine the consequences of
if (grep $_ == 5, 1 .. 10_000) { ... }
You've just scanned 99,995 more elements than necessary!
The Perl FAQ suggests use of a hash. See my response to this same
question.
--
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 **
<stu> what does y/// stand for? <tenderpuss> why, yansliterate of course.
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