my @columns; # this is your result.
    # each element will be an array(ref) of cell values.

    for(my $iC = $oWkS->{MinCol};
        defined $oWkS->{MaxCol} && $iC <= $oWkS->{MaxCol};
        $iC++
    ) {
        for(my $iR = $oWkS->{MinRow}; 
            defined $oWkS->{MaxRow} && $iR <= $oWkS->{MaxRow};
            $iR++
        ) {
            my $oWkC = $oWkS->{Cells}[$iR][$iC];
            $columns[$iC][$iR] = $oWkC ? $oWkC->Value : undef;
        }
    }