Answers for "count distinct column in groupy pandas"

pandas groupby column count distinct values

# Pandas group by a column looking at the count unique/count distinct values of another column

df.groupby('param')['group'].nunique()

pandas count distinct values in column

#column name ISSDTM
pd.to_datetime(df.ISSDTM, errors='coerce').dt.year

#result
0    2013
1    2013
2    2009
3    2009
Name: ISSDTM, dtype: int64