in reply to how to set a value for a hash reference

The easiest thing is not to set the default, but apply the default while reading the value in the end, like my $ov = $overlap->{$a}{$b} // 0 (requires perl 5.10 or newer, but older versions than 5.12 aren't maintained anyway).

By the way a nicer way to write the inner loops is 

my $last = @members - 1;
for my $i (0 .. $last) {
    for my $j ($i + i .. $last) {
        $overlap->{$members[$i]}{$members[$j]}++;
        $overlap->{$members[$j]}{$members[$i]}++;
    }
}

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Perl 6 - second systems done right

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Re^2: how to set a value for a hash reference
by AWallBuilder (Beadle) on Mar 14, 2012 at 13:17 UTC

    thank you for the details and the loop suggestion. The "//" means if for a and b overlap doesn't exist then it equals zero, right?

    But where would I put this line? after the loop? no -> between the $a and $b? would I have to embed it in a loop with a and b being all elements of members?

[reply]
      The "//" means if for a and b overlap doesn't exist then it equals zero, right?

      Correct. It's the "defined-or" operator.

      But where would I put this line? after the loop?

      Wherever your read the values of $overlap.

      Perl 6 - second systems done right
[reply]
[d/l]

        hmmm - I guess its a bit complicated because I"m just passing the entire hash reference to another script that writes the output in a nice matrix format. And I don't want to modify "write_R_matirx". any other suggestions? 

        use Smash::Utils::MatrixIO qw(:all);
my $SMASH_overlap_file="$CDHIT_file.smash.overlap";
write_R_matrix($SMASH_overlap_file,$overlap);

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[reply]
[d/l]

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