calculate_fisher        Calculate direct index according to the Fisher
                        hedonic double imputation method
calculate_geometric_average
                        Calculate the geometric average of a series of
                        values
calculate_laspeyres     Calculate direct index according to the
                        Laspeyres hedonic double imputation method
calculate_paasche       Calculate direct index according to the Paasche
                        hedonic double imputation method
calculate_price_index   Calculate index based on specified method
                        (Fisher, Laspeyres, Paasche, HMTS)
custom_update_function
                        Default update function
data_constraxion        A real estate example dataframe
