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.
Cet exercice fait partie du cours
Data Manipulation with data.table in R
Instructions
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.
Exercice interactif pratique
Essayez cet exercice en complétant cet exemple de code.
# Add the mean_duration column
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