push @{ $this_hash{$key} }, $something;

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Perl will automagically create a new anonymous array and associate it with $this_hash{$key}, even if the hash didn't even have this key before (it's called 'autovivification'). OTOH, if the key is already pointing to an array, Perl will reuse it.

In reply to Re^3: Help !!! Symbolic Math Factroize Subroutine is clobbering my hash by Anonymous Monk
in thread Help !!! Symbolic Math Factroize Subroutine is clobbering my hash by ipreferperl

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