map { MAPCLAUSE } grep { GREPLCAUSE }
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Can be rewritten as:

map { GREPCLAUSE ? MAPCLAUSE : () }
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For instance, if you want a list of the squares of the first five odd numbers, either of these will work.

@odds_squared = map { $_**2 } grep { $_%2 } 1..10;
@odds_squared = map { $_%2 ? $_**2 : () } 1..10;

Result: 1 9 25 49 81
[download]

-Blake