We have seen how we can implement the split-apply-combine approach on a data frame using three lines of code. The
plyr package helps us to implement the approach in one line. Since R has multiple data structures, we need multiple functions to work on different data structures. R has three main data structures: list, array, and data frames. So, there could be three different types of input, and the output could produce three different types of data structures. There could be
3 x 3 = 9 possible input-output combinations, and for this reason,
9 functions to incorporate all the input-output combinations. In addition, we have three additional functions that take six different types of input but display ...