groupby apply assign pandas

groupby 한 결과에 column 추가하고 싶을 때

(df
.loc[lambda df: df.unique_apt.isin(l_unique_apt_gn)]
.groupby(['unique_apt'])
.apply(lambda gdf: gdf.assign(min_trade_date=lambda df: df.trade_date.min()))
.sort_values('min_trade_date')
)

Ref

• https://stackoverflow.com/questions/30244952/how-do-i-create-a-new-column-from-the-output-of-pandas-groupby-sum