Computing stats by groups (I)
So far you have worked with the two dimensions, rows and columns of a data.table. It's now time to consider the virtual third dimension by dividing rows into groups to calculate statistics.
Cet exercice fait partie du cours
Data Manipulation with data.table in R
Instructions
Compute the mean duration for every start_station, calling the aggregated column mean_duration.
Exercice interactif pratique
Essayez cet exercice en complétant cet exemple de code.
# Compute the mean duration for every start_station
mean_start_stn <- batrips[, .(___), by = ___]
mean_start_stn