Returning more (or less even) elements than provided is very natural for map and very commonly used, especially for generating hashes ..

For those not familiar with returning less -- use an empty list (). To build on davidrw's example:

perl -MData::Dumper -le 'my %oddcubes = map { $_%2 ? ($_ => $_**3) : (
+) } 1..9; print Dumper \%oddcubes'
$VAR1 = {
          '1' => 1,
          '3' => 27,
          '7' => 343,
          '9' => 729,
          '5' => 125
        };
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