Cannot concatenate more than 3 elements in an expression for ggplot2's geom_text

Question

I have a data frame for which I\'m computing a linear model and would like to include the correlation coefficient and its significance using geom_text.

struc         


        

Answer 1

pp + geom_text(aes(x=20, y=-5,
  label=paste("list(italic(r) ==", round(val$estimate, digits=2), ", p < 0.0001)")),
  parse=TRUE, colour="black")

The key is that the label argument is parsed if parse==TRUE, this means that the texts need to have a same format as in ?plotmath.

What the geom_text exactly do is like this:

expr <- parse(text=label)

and then draw text using the expr as a label. So label argument need to be a valid expression. In you example,

paste("italic(r) ==", 3, "Q", sep=" ")

is invalid expression, so

parse(text=paste("italic(r) ==", 3, "Q", sep=" ")) 

induces an error.

In plotmath, if you want to concat symbols, then you need to use:

paste(x, y, z)
list(x, y, z)

So if you want to simply concat, then

geom_text(foobar, label=paste("paste(italic(r) ==", 3, "Q)", sep=" "))

The first (outside) paste concats a piece of texts into one text variable. The second (inside) paste is used in plotmath process.

In my example above, I used list (see ?plotmath) instead of paste, because stats and p value is separated by `,'.