Whenever I see a "sum this if that matches" type problem, I always think hash.

Given your 2-d array above, how about:

my %sums;

for( my $i = 0; $i < $lines; ++$i )
{
    $sums{$data[$i][1]} += $data[$i][3];
}

[download]

The %sums hash now contains the sums keyed by the day (if I'm understanding what field 1 is).

Personally, I would tend to write this much more compactly, but this should work and is easier to understand.

Update: fixed stupid typoes. (Thanks JadeNB).

G. Wade

In reply to Re: Silly array-ish question. by gwadej
in thread Silly array-ish question. by fleurdmiller

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