Modern R Programming Cookbook

There's more…

You might think that we could use the newly defined function within the dplyr framework just like the other function inside the summarize() function, but there is a problem in using the multi-valued function within summarize(). Here is an example of the use of the customized multi-valued function within the summarize() function:

    desStat <- USAairlineData2016 %>%    select(MONTH, ORIGIN, DEP_DELAY) %>%    group_by(ORIGIN, MONTH) %>%    summarise(      fourNumSum(DEP_DELAY)    )

If you run the preceding code, you will get an error as shown in the following screenshot:

The summarise() verb is expecting a function that can produce a single-valued ...