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.
Deze oefening maakt deel uit van de cursus
Data Manipulation with data.table in R
Oefeninstructies
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.
Praktische interactieve oefening
Probeer deze oefening eens door deze voorbeeldcode in te vullen.
# Add the mean_duration column
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