.groupby & .fillna with median

Question

# Create a groupby object: by_sex_class
by_sex_class = titanic.groupby([\"sex\",\"pclass\"]).count()

# Write a function that imputes median
def impute_median(series):
          


        

Answer 1

The new values are matched to the original dataframe by the index (when you group, you still keep the original index).

df['age'] = df.groupby(["sex","pclass"])['age'].transform(lambda x: x.fillna(x.median()))

Answer 2

I will recommend using this

df['age'].fillna(df.groupby(["sex","pclass"])['age'].transform('median'),inplace=True)