The Art of R Programming

More on c()

In this section, we’ll discuss a couple of miscellaneous facts related to the concatenate function, c(), that often come in handy.

If the arguments you pass to c() are of differing modes, they will be reduced to a type that is the lowest common denominator, as follows:

> c(5,2,"abc")
[1] "5"   "2"   "abc"
> c(5,2,list(a=1,b=4))
[[1]]
[1] 5

[[2]]
[1] 2

$a
[1] 1

$b
[1] 4

In the first example, we are mixing integer and character modes, a combination that R chooses to reduce to the latter mode. In the second example, R considers the list mode to be of lower precedence in mixed expressions. We’ll discuss this further in Section 4.3.

You probably will not wish to write code that makes such combinations, but you may encounter code in which this ...