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.
Este exercício faz parte do curso
Data Manipulation with data.table in R
Instruções do exercício
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.
Exercício interativo prático
Experimente este exercício completando este código de exemplo.
# Add the mean_duration column
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