in reply to Re: Multidimensional Hash implementation/usage
in thread Multidimensional Hash implementation/usage

The second possibility is to use a separator to join the indexes. Be sure that the separator doesn't occur in the indexes: 
my $idx = substr $Fld57, 3, 5;
$CNT{$idx . $Fld1 . $Fld15}++;
$COST{$idx . $Fld1 . $Fld15} += $Fld14;

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Actually, Perl offers some syntactic sugar just for that:

$foo{$a, $b, $c} is equivalent to $foo{join($;, $a, $b, $c)}

It is documented in perlvar.

In Section Seekers of Perl Wisdom