r - 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 quotes?

For example, this works:

qplot(x,y,data=a)

But this does not:

qplot("x","y",data=a)

I ask because I often have data matrices with spaces in the name. Eg, "State Income". ggplot2 needs data frames; ok, I can convert. So I'd want to try something like:

qplot("State Income","State Ideology",data=as.data.frame(a.matrix))

That fails.

Whereas in base R graphics, I'd do:

plot(a.matrix[,"State Income"],a.matrix[,"State Ideology"])

Which would work.

Any ideas?

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.