Pandas percentage of total with groupby

Question

This is obviously simple, but as a numpy newbe I'm getting stuck.

I have a CSV file that contains 3 columns, the State, the Office ID, and the Sales for that office.

I want to calculate the percentage of sales per office in a given state (total of all percentages in each state is 100%).

df = pd.DataFrame({'state': ['CA', 'WA', 'CO', 'AZ'] * 3,
                   'office_id': list(range(1, 7)) * 2,
                   'sales': [np.random.randint(100000, 999999)
                             for _ in range(12)]})

df.groupby(['state', 'office_id']).agg({'sales': 'sum'})

This returns:

                  sales
state office_id        
AZ    2          839507
      4          373917
      6          347225
CA    1          798585
      3          890850
      5          454423
CO    1          819975
      3          202969
      5          614011
WA    2          163942
      4          369858
      6          959285

I can't seem to figure out how to "reach up" to the state level of the groupby to total up the sales for the entire state to calculate the fraction.

Answer 1

Update 2022-03

This answer by caner using transform looks much better than my original answer!

df['sales'] / df.groupby('state')['sales'].transform('sum')

Thanks to this comment by Paul Rougieux for surfacing it.

Original Answer (2014)

Paul H's answer is right that you will have to make a second groupby object, but you can calculate the percentage in a simpler way -- just groupby the state_office and divide the sales column by its sum. Copying the beginning of Paul H's answer:

# From Paul H
import numpy as np
import pandas as pd
np.random.seed(0)
df = pd.DataFrame({'state': ['CA', 'WA', 'CO', 'AZ'] * 3,
                   'office_id': list(range(1, 7)) * 2,
                   'sales': [np.random.randint(100000, 999999)
                             for _ in range(12)]})
state_office = df.groupby(['state', 'office_id']).agg({'sales': 'sum'})
# Change: groupby state_office and divide by sum
state_pcts = state_office.groupby(level=0).apply(lambda x:
                                                 100 * x / float(x.sum()))

Returns:

                     sales
state office_id           
AZ    2          16.981365
      4          19.250033
      6          63.768601
CA    1          19.331879
      3          33.858747
      5          46.809373
CO    1          36.851857
      3          19.874290
      5          43.273852
WA    2          34.707233
      4          35.511259
      6          29.781508