Computing stats by groups (II)

When grouping a data.table by multiple columns, you need to specify the by argument as either a character vector or a list. In this exercise, you will calculate the mean of duration for:

Each unique combination of start_station and end_station
Each start_station for each month

Deze oefening maakt deel uit van de cursus

Data Manipulation with data.table in R

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Praktische interactieve oefening

Probeer deze oefening eens door deze voorbeeldcode in te vullen.

# Compute the mean duration for every start and end station
mean_station <- batrips[, ___, ___ = .(___, ___)]
mean_station

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