Question

I’d like to write an axis label over two lines with an expression() statement. However, plotmath and expression won’t allow this (e.g. subscripted text appears on the far right). I found this discussion circa 2005 of a similar issue but the work around that they offer doesn’t translate to my application in ggplot2. A recent question addressed a different permutation of multi-line expression statements, but again the work around provided doesn’t apply here.

Example:

p <- ggplot(mtcars,aes(x=wt,y=mpg))+
  geom_point()+
  xlab(expression(paste("A long string of text goes here just for the purpose \n of illustrating my point Weight "[reported])))
try(ggsave(plot=p,filename=<some file>,height=4,width=6))

yields an image where subscript “reported” is kicked out to the right when I’d like it to sit next to the previous word.

Answer 1

I think this is a bug. (Or a consequence of the fact that “multi-line expressions are not supported”, as stated in the conversation you linked to).

The workaround that Gavin Simpson alluded to is:

#For convenience redefine p as the unlabeled plot
p <- ggplot(mtcars,aes(x=wt,y=mpg))+geom_point()

#Use atop to fake a line break
p + xlab(expression(atop("A long string of text for the purpose", paste("of illustrating my point" [reported]))))

It is possible to use true line breaks with subscripts. In the short example below, which has the same form as your example, the subscript is correctly placed adjacent to the rest of the text but the two lines of text are not centered correctly:

p + xlab(expression(paste("line1 \n line2 a" [b])))

I think that in both cases, the subscript is placed wrong when the upper line of text is longer than the lower line of text. Compare

p + xlab(expression(paste("abc \n abcd" [reported])))

p + xlab(expression(paste("abc \n ab" [reported])))

The subscript always ends up aligned just to the right of the right end of the upper line.

p + xlab(expression(paste("abcdefghijklmnop \n ab" [reported])))