I don't really see the need or usefulness of the first file and array. Personally, on this specific case, I would use two hashes, one for the "+" values and one for the "-" values, because I do not think that a two-level data structure brings very much for this. This is my proposal: 
use strict;
use warnings;

my (%plus, %minus);
while (<DATA>) {
    my ($fruit, $sign) = split;
    if ($sign eq '+') {
        $plus{$fruit} = 1;
    } else {
        $minus{$fruit} = 1;
    }
}

print "Positives are : ", (map "$_, ", keys %plus), "\n";
print "Negatives are : ", (map "$_, ", keys %minus), "\n";

__DATA__
apple    +
cherry    -
cherry    +
peach    +
banana    -

[download]
This yields the following output: 
$ perl plus_minus.pl
Positives are : peach, cherry, apple,
Negatives are : banana, cherry,

[download]
As you can see, real code is about 12 lines or so.

In reply to Re: Unique key identifer? by Laurent_R
in thread Unique key identifer? by lecb

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