How to refer to a variable name with spaces?

Question

In ggplot2, how do I refer to a variable name with spaces?

Why do qplot() and ggplot() break when used on variable names with

Answer 1

Answer: because 'x' and 'y' are considered a length-one character vector, not a variable name. Here you discover why it is not smart to use variable names with spaces in R. Or any other programming language for that matter.

To refer to variable names with spaces, you can use either hadleys solution

a.matrix <- matrix(rep(1:10,3),ncol=3)
colnames(a.matrix) <- c("a name","another name","a third name")

qplot(`a name`, `another name`,data=as.data.frame(a.matrix)) # backticks!

or the more formal

qplot(get('a name'), get('another name'),data=as.data.frame(a.matrix))

The latter can be used in constructs where you pass the name of a variable as a string in eg a loop construct :

for (i in c("another name","a third name")){
    print(qplot(get(i),get("a name"),
      data=as.data.frame(a.matrix),xlab=i,ylab="a name"))
    Sys.sleep(5)
}

Still, the best solution is not to use variable names with spaces.

Answer 2

Using get is not more "formal", actually I would argue the opposite. As the R help says (help("`")), you can almost always use a variable name that contains spaces, provided it's quoted. (Normally, with a backtick, as already suggested.)

Answer 3

Something similar was asked on ggplot2 mailing list and Mehmet Gültaş linked to this post. Another way of using strings to construct your ggplot call is through the aes_strings function. Note that you still have to put backticks inside the quotes for the thing to work for variables with spaces.

library(ggplot2)

names(mtcars)[1] <- "em pi dzi"

ggplot(mtcars, aes_string(x = "cyl", y = "`em pi dzi`")) +
  theme_bw() +
  geom_jitter()