Adding multiple columns (I)

More often than not, you may want to add/update multiple columns by reference. There are two ways to do this in data.table:

LHS := RHS form
Functional form

In this exercise, you will add columns using the LHS := RHS form. In the LHS, you specify column names as a character vector and in the RHS, you specify values/expressions to be added inside list() (or the alias, .()).

Deze oefening maakt deel uit van de cursus

Data Manipulation with data.table in R

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Oefeninstructies

Add two new columns (mean_duration and median_duration) by reference using the LHS := RHS form that calculates the mean and median of the duration column for every start_station.

Praktische interactieve oefening

Probeer deze oefening eens door deze voorbeeldcode in te vullen.

# Add columns using the LHS := RHS form
batrips[, ___, 
        by = start_station]

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