Pandas Groupby How to Show Zero Counts in DataFrame

问题

I have the following Pandas dataframe:

Name   | EventSignupNo | Attended | Points
Smith  | 0145          | Y        | 20.24
Smith  | 0174          | Y        | 29.14
Smith  | 0239          | N        | 0
Adams  | 0145          | N        | 0
Adams  | 0174          | Y        | 33.43
Morgan | 0239          | Y        | 31.23
Morgan | 0244          | Y        | 23.15

and what I'd like is a count of the number of events attended and not attended per person, and the sum of their points, per person. So I do a groupby: df.groupby([Name, Attended]).agg({"Attended": "count", "Points": "sum"}).rename(columns = {"Attended: "Count"}).reset_index()

which would give me something like:

Name   | Attended | Count | Points
Smith  | Y        | 2     | 49.38
Smith  | N        | 1     | 0
Adams  | Y        | 1     | 33.43
Adams  | N        | 1     | 0
Morgan | Y        | 2     | 54.38

but I'd want something like:

Name   | Attended | Count | Points
Smith  | Y        | 2     | 49.38
Smith  | N        | 1     | 0
Adams  | Y        | 1     | 33.43
Adams  | N        | 1     | 0
Morgan | Y        | 2     | 54.38
Morgan | N        | 0     | 0

I tried playing around with pd.MultiIndex to try to fill the missing zero count, but to no avail. I've read the other similar questions but I'm having trouble dealing with the continuous Points column using MultiIndex. Any idea how to do this?

回答1:

You could do this with groupby + agg. For your exact output with Y and N at each level, you'd need reindex:

g = df.groupby(['Name', 'Attended'], sort=False).Points.agg(['count', 'sum'])

g
                 count    sum
Name   Attended              
Smith  Y             2  49.38
       N             1   0.00
Adams  N             1   0.00
       Y             1  33.43
Morgan Y             2  54.38

idx = pd.MultiIndex.from_product([g.index.levels[0], ['Y', 'N']])

idx
MultiIndex(levels=[['Adams', 'Morgan', 'Smith'], ['N', 'Y']],
           labels=[[2, 2, 0, 0, 1, 1], [1, 0, 1, 0, 1, 0]])


g.reindex(idx, fill_value=0)

          count    sum
Smith  Y      2  49.38
       N      1   0.00
Adams  Y      1  33.43
       N      1   0.00
Morgan Y      2  54.38
       N      0   0.00

来源：https://stackoverflow.com/questions/47372181/pandas-groupby-how-to-show-zero-counts-in-dataframe