Question

I recently saw a function in R where someone had used . as an argument. I can’t seem to find any documentation on this (other than the use of ellipsis or “dot-dot-dot”). Can someone either point me in the direction of documentation or provide an example of usage?

hello.world <- function(.) "Hello World"
# function(.) is what I'm asking about.

Answer 1

Dot is a a valid character in symbol names just like any letter, so . is no different than let’s say a – it has no special meaning in this context. You can write things like:

> . <- 10
> . + .
[1] 20

It may look strange but is valid in R. The above use function(.) is let’s say unusual, but syntactically valid. Since the author did not reference . in the function body, we will never know if he meant ... or just used it because he could.