Andrew Treadway covers a few of the lesser-known apply functions in R:

rapplyLet’s start with

rapply. This function has a couple of different purposes. One is to recursively apply a function to a list. We’ll get to that in a moment. The other use ofrapplyis to a apply a function to only those elements in a list (or columns in a data frame) that belong to a specified class. For example, let’s say we have a data frame with a mix of categorical and numeric variables, but we want to evaluate a functiononlyon the numeric variables.

Click through for some examples of `rapply`

as well as `vapply`

and `eapply`

. I’ve used `rapply`

to get cardinality of each feature in a data frame but the other two are new to me. H/T R-bloggers