CODE EXAMPLE FOR PYTHON

pandas fill missing values with average

# Fill colB na's with avg of colA Groupings 
df.groupby('colA')['colB'].transform(lambda value: value.fillna(value.mean()))
# Fill missing Lot Frontage with avg for Neighborhood 
df.groupby('Neighborhood')['Lot Frontage'].transform(lambda value: value.fillna(value.mean()))