What does the symbol "%<>%" do in R?

Question

I see this symbol: %<>%, in someone's R code and could not find out what it does by googling. Can anyone help shed some light on this?

Answer 1

Functions surrounded by percent symbols such as %<>%, %in%, %over%, %*%, etc. are called infix operators and, as pointed out by @RichardScriven, can be found in the manual by surrounding them with backticks or quotation marks: ?"%<>%" or ?`%<>%` should both bring you to the help pages (GitHub version here; here's the source code)

You can define your own a la:

"%+%" <- function(s1, s2) paste0(s1, s2)
"%U%" <- function(A, B) union(A, B)

And so on. Here's the relevant chapter in Hadley Wickham's book.