Level 3: Aggregating · Exercise 37 of 63 · Pro

Fill missing values with the group mean

A pandas exercise from Pandasdrill. Solve it with a Python editor in your browser running real pandas, and it is checked the moment you submit.

The task

Some players have no `score`. Fill each missing score with the mean score of that player's team (computed from the team's known scores) and return the `score` column as a Series.

What this exercise teaches

fillna accepts a Series and uses the value with the matching label for each gap, so transform("mean") supplies each row its own team's mean. mean skips NaN, so the known scores define the fill. Filling with the overall mean ignores the team, and returning the transform alone overwrites the real scores too.

A hint if you get stuck

Build a Series of team means aligned to every row with transform("mean"), then pass it to fillna.