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pythonpandasdataframecountunique

Groupby and count the number of unique values (Pandas)

I have a dataframe with 2 variables: ID and outcome. I'm trying to groupby ID first, and count the number of unique values of outcome within that ID. 

df
ID    outcome
1      yes
1      yes
1      yes
2      no
2      yes
2      no

Expected output:

ID    yes    no
1      3     0
2      1     2

My code df[['PID', 'outcome']].groupby('PID')['outcome'].nunique() gives the number of the unique value itself, such that:

ID
1   2
2   2

But I need the counts of the yes and no, how can I achieve that? Thanks!

Solution

  • How about pd.crosstab?

    In [1217]: pd.crosstab(df.ID, df.outcome)
Out[1217]: 
outcome  no  yes
ID              
1         0    3
2         2    1