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I want to plot a label that looks like this in ggplot2:

Value is $\sigma$, R^{2} = 0.6 where Value is is ordinary font, $\sigma$ is a Greek lowercase sigma letter and R^{2} = 0.6 appears as an R with a superscript 2 followed by equal sign (=) followed by 0.6. How can this be used in ggplot factors and in arguments to things like xlab,ylab of R?

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2 Answers 2

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80

Something like this :

g <- ggplot(data=data.frame(x=0,y=0))+geom_point(aes(x=x,y=y))
g+ xlab( expression(paste("Value is ", sigma,",", R^{2},'=0.6')))

EDIT

Another option is to use annotate with parse=T:

g+ annotate('text', x = 0, y = 0, 
        label = "Value~is~sigma~R^{2}==0.6 ",parse = TRUE,size=20)

enter image description here

EDIT

The paste solution may be useful if the constant 0.6 is computed during plotting. 

r2.value <- 0.90
g+ xlab( expression(paste("Value is ", sigma,",", R^{2},'=',r2.value)))
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10 Comments

If you want the sigma try using \u03c3
paste never strikes me as a good option in plotmath; try xlab( bquote(Value~is~sigma~R^{2}==.(r2.value))) instead.
In case anybody is unaware of this, baptiste is a true plotmeister. If you want to learn a lot about R's plotting systems, just pull up his many answers on SO and study from a master.
I am not sure whether I should start another question but "r2.value; ..." did not work for me. Instead of 0.9, the xlab showed re.value. Am I doing something wrong? Using bquote works. Many thanks
What do you mean by "during plotting"? I did this, but get text "r2.value", but not its value.
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52

Somewhat more straightforward than paste() might be:

g <- ggplot(data=data.frame(x=0,y=0))+geom_point(aes(x=x,y=y))
 g + xlab( expression(Value~is~sigma~R^{2}==0.6))
 # ~ for spaces, and * for no-space between (unquoted) expressions

Generally paste and all those paired-quotes are not needed if you use the proper plotmath connectives. Even if you want the text that would otherwise create a Greek letter, all you need to do is enclose it in quotes with either a * or ~ on each side. One trouble with offering paste to newcomers to plotmath expressions is that they then think it is the same as paste in the rest of the language.

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2 Comments

I think the 'labels' argument to annotate takes a character mode You could look up what Unicode value 'sigma' might have in the sans-serif font you have installed.
Side note for lattice users : This solution works also for lattice plot. .i.e xyplot(y~x,dat=data.frame(x=0,y=0),xlab=expression(Value~is~sigma~R^{2}==0.6))