Adding columns by group
Recall that you can perform computations by group using the by
argument of the data.table
. In this exercise, you will add new columns by group to the original data.table
by reference.
This exercise is part of the course
Data Manipulation with data.table in R
Hands-on interactive exercise
Have a go at this exercise by completing this sample code.
# Add a new column equal to total trips for every start station
batrips[, ___, by = ___]