Helper method to aggregate hit rate calculations

[copelco]

Example:

group_by = {"driver_race"}
df = query.contraband_query(agency_id=80, group_by=group_by)
chart = query.hit_rate_chart(df, group_by=group_by)
table = query.hit_rate_table(df, group_by=group_by)
chart

Returns:

{'Asian': [20.24],
 'Black': [27.66],
 'Hispanic': [17.13],
 'Native American': [23.33],
 'Other': [24.49],
 'White': [21.39]}