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# if @ds1_rows is an AofA holding a dataset, then...
for my $a ( @ds1_rows ) {
...
                    # and then, not using $aref... 
                    # instead, you are using $a again
                    my $record2 = "@$a";

#Simple solution for union and intersection
foreach $e (@a) { $union{$e} = 1 }
...
}
@union = keys %union;
@isect = keys %isect;