in_array_unique_combis= numpy array of unique combinations of taxonomy* (i.e. taxonomy considering all parameters enumerated in get_list_for_grouping)
in_position_of_unique= its length is the same as the number of rows in in_df; for each row, it indicates the corresponding element of in_array_unique_taxonoms
in_country_adm_ids= an array of strings with length equal to the number of rows in in_df. It indicates the country_admin_ID each row in in_df is coming from.
out_df= Pandas DataFrame in which a certain combination of taxonomy* only exists once (the different rows of in_df for the same combination of taxonomy*
have been grouped together). Note that the number of buildings (i.e. "number" or "buildings" column), number of dwellings and number of people
("occupants_per_asset") are the only values that are added, all other values (e.g. "dwell_per_bdg") are values per building or dwelling and are