@staticmethod
def _max_form(f, colname):
    """
        Assumes dataframe with hierarchical columns with first index equal to the
        use and second index equal to the attribute.

        e.g. f.columns equal to::

            mixedoffice   building_cost
                          building_revenue
                          building_size
                          max_profit
                          max_profit_far
                          total_cost
            industrial    building_cost
                          building_revenue
                          building_size
                          max_profit
                          max_profit_far
                          total_cost
        """
    df = f.stack(level=0)[[colname]].stack().unstack(level=1).reset_index(level
        =1, drop=True)
    return df.idxmax(axis=1)
