How to use apply with groupby in pandas

apply_groupby.py

# grooop
grouped = with_region.groupby('level_comp_region')

# How many workers are in which 
res = (
    grouped
    .apply( lambda grp: pd.Series({
        "old_min": grp["old_min"].iloc[0],
        "old_max": grp["old_max"].iloc[0],
        "employees here": len(grp)
        }))
    .sort_values(['employees here'])
    .reset_index()

)

res.head(3)