Great, but this isn't a very helpful format for a human being... There's a nicer way of displaying weekdays:
trucks$departure_weekday <- wday(trucks$departure_date, label=TRUE, abbr=FALSE)
The label argument makes the function display the weekdays in a human-readable format and the abbr argument set to FALSE tells R that weekdays shouldn't be in abbreviated form.
Use the wday() function on the departure_date column in the ships data set to overwrite the departure_weekday column. This time let's make R save this information in a human-readable format and in an unabbreviated form (that is, we want to see "Monday" instead of "Mon").
