in reply to Re^2: Grouping an array of hashrefs by similar key values
in thread Grouping an array of hashrefs by similar key values
It aliases $item to $items{ $row->{item_key} }. Changes to one affect both. I could have done $item_ref = \( $items{ $row->{item_key} } );, but it made the subsequent code rather messy (but not as much as using neither).