I would write: 
@flat = grep {defined} map {@$_} grep {$_} @AoA;

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This assumes each element of @AoA is either an arrayref, or an undefined value.

I'm not the biggest fan of using EXPR ? LIST : () inside a map just to avoid writing grep.

In reply to Re: Flatten sparse AoA by JavaFan
in thread Flatten sparse AoA by FloydATC

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