How to get percentage contribution for each group in df having MultiIndex in pandas?

Question

I have a df as below:

year and Continent are indexes. hydro_total is a column.

I want to add a column that will have a percentage of contribution of the continent for the given year.

For example: For the year 1971, Africa has 2.04 contribution and America has 48.56 contributions, similarly for Asia, Europe and Oceania. This will repeat for each year.

Here is the data:

{'hydro_total': {(1971, 'Africa'): 1861980.0,
  (1971, 'America'): 44127920.0,
  (1971, 'Asia'): 14514450.0,
  (1971, 'Europe'): 28232850.0,
  (1971, 'Oceania'): 2126000.0,
  (1972, 'Africa'): 2300750.0,
  (1972, 'America'): 47242190.0,
  (1972, 'Asia'): 14970150.0,
  (1972, 'Europe'): 29427610.0,
  (1972, 'Oceania'): 2225000.0}}

Answer 1

If I understand you correctly:

df['contribution'] = df.groupby(level=0)['hydro_total'] \
                       .transform(lambda g: g / g.sum()) * 100

Result:

              hydro_total  contribution
1971 Africa     1861980.0      2.049212
     America   44127920.0     48.565228
     Asia      14514450.0     15.973959
     Europe    28232850.0     31.071820
     Oceania    2126000.0      2.339781
1972 Africa     2300750.0      2.392485
     America   47242190.0     49.125821
     Asia      14970150.0     15.567037
     Europe    29427610.0     30.600942
     Oceania    2225000.0      2.313715