map works like a function call. It returns the last thing executed in the block. And if that was the failure of a defined test, then it is a false value. The statement you wanted is: 
my %hash2 = map {defined($hash1{$_}) ? ($_ => $hash1{$_}) : ()} @ary;

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But note that I would avoid this with large arrays unless you are on 5.6.1 or better.

In reply to Re (tilly) 1: Mapping array over a hash by tilly
in thread Mapping array over a hash by agoth

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