mapping.py

## Reverse the mapping to match with the food values
map_dict_reverse = {val:key for key,vals in map_dict.items() for val in vals}

##==== Mapping trick: func Map() to work with Pandas SERIES; fillna = 'others'
dairy_table['Food_Category'] = dairy_table['Food'].map(map_dict_reverse).fillna('others')

Out[134]: 
index0        Milk
index1      others
index2        Milk
index3        Milk
index4        Milk

##==== Mapping trick: func Applymap() to work with Pandas DATA FRAME; 
##====                keep the raw values if not defined in the dict
dairy_table.applymap(lambda x: map_dict_reverse.get(x) if x in map_dict_reverse.keys() else x)

Out[139]: 
                                    Food     Measure Grams Calories
index0                              Milk       1 qt.   976      660
index1                              Milk       1 qt.   984      360 
......
index10                            Cocoa       1 cup   252      235
index11  Yogurt, of partially skim. milk       1 cup   250      128
index12                          Pudding       1 cup   248      275