Exercise

Computing in j (III)

In the previous exercise, you were able to pass expressions in j that returned a vector. Recall that if you want to return a data.table instead, wrap the expression with list() (or it's alias, .()). This lets you:

Rename the column result
Compute more than one expression on a column
Compute on more than one column

Instructions 1/3

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1
Calculate the average duration as a one-column data.table with the column name mean_durn.
2
Calculate the minimum and maximum duration (don't rename the columns).
3
Find the average duration and the date of the last ride (using the end_date column). Name these columns mean_duration and last_ride, respectively.