coldy has asked for the wisdom of the Perl Monks concerning the following question:

Hi Monks, I would like to emulate 
 fgrep -w -f list.txt largefile.txt

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but the results must be in the same order as they appear in list.txt. I have tried 
my @list = <$list>;

my @large = <$large>;

foreach my $test (@list){
        print grep (/^$test/,@large);

}

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but this does not work... the file $list is a single field and the file $large has several fields but is matched to $list by the first field. Any advice would be appreciated. Thanks..

Replies are listed 'Best First'.
Re: emulate "fgrep -f file" with results ordered by "file"
by toolic (Bishop) on Mar 15, 2011 at 02:10 UTC
    but this does not work...
    That is not descriptive enough, and you haven't shown enough of your code, but here are a couple suggestions:
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      thanks for the suggestion - chmop worked. There is one other problem - it is fairly slow. There are about 1M itmes to grep from @list and @large has a few more lines than that (about 1.2M )..any ideas on how to do this more efficiently?
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        You could create an index (=hash lookup table) by the first field of 'large'.  Then loop over @list and check if the key exists in the lookup table.

        Something like 

        my %index;
while (<DATA>) {   # your $large
    my ($f1) = split;
    $index{$f1} .= $_;
}

my @list = qw(foo r2c1 bar r3c1);
for (@list) {
    print $index{$_} if exists $index{$_};
}

__DATA__
r1c1 r1c2 r1c3
r2c1 r2c2 r2c3
r3c1 r3c2 r3c3

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