Exercise

Combining i, j, and by (II)

As you did in the last chapter, you will combine the i, j, and by arguments, but this time modify the existing data.table by reference in j.

Instructions

100 XP

For all rows where duration is greater than 600, group batrips by start_station and end_station to add a new column (mean_duration) by reference which calculates the mean duration of all trips.