The Art of R Programming

No Pointers in R

R does not have variables corresponding to pointers or references like those of, say, the C language. This can make programming more difficult in some cases. (As of this writing, the current version of R has an experimental feature called reference classes, which may reduce the difficulty.)

For example, you cannot write a function that directly changes its arguments. In Python, for instance, you can do this:

>>> x = [13,5,12]
>>> x.sort()
>>> x
[5, 12, 13]

Here, the value of x, the argument to sort(), changed. By contrast, here’s how it works in R:

> x <- c(13,5,12)
> sort(x)
[1]  5 12 13
> x
[1] 13  5 12

The argument to sort() does not change. If we do want x to change in this R code, the solution is to reassign the arguments:

> x ...