Concatenate Strings and Expressions in a Plot's Title

Concatenate strings and expressions in a plot's title

You want to read ?plotmath to see how to do this sort of thing. Here is an example:

plot(1:10, main = expression(ARL[1] ~ "curve for" ~ S^2))

The [.] is subscript, whilst ^ gives superscript. The ~ spaces out the parts of the expression as if there were literal spaces.

Edit: normally I would have done:

plot(1:10, main = expression(ARL[1] ~ curve ~ for ~ S^2))

but that throws an error because for is being interpreted as the start of a for() loop call.

combine expression objects into a single text string for ggplot labels

We can wrap it within bquote

library(ggplot2)
ggplot() +
 geom_point(data = iris, aes(x = Sepal.Length, y = Sepal.Width)) +
   labs(x = bquote('Static text: '~.(sup)~.(sub)))

-output

How to concatenate two expressions?

... found an answer (thanks to a previous post which was deleted):

expr <- bquote(bgroup("(",frac(1,3)*", "*frac(1,2),")")) 
plot(0, 0, xlab = bquote(alpha~"is in "~.(expr)), ylab = "")

Vectorizing a concatenated text label for a plot

You can swap expression for bquote which has a different use of italic and allows using .() to evaluate an object. I discovered this use here. Then I use a for loop as a workaround for the desired vectorized functionality.

plot.new(); axis(1); axis(2)

txt <- list(x = c(0.5, 0.5), y = c(0.8, 0.4), vals = c(0.01, 0.001))

for(i in 1:length(txt$vals)){
  text(x = txt$x[i], 
       y = txt$y[i], 
       labels = bquote(paste(italic("P"), "-trend = ", .(txt$vals[i]))))
}

Combining paste() and expression() functions in plot labels

An alternative solution to that of @Aaron is the bquote() function. We need to supply a valid R expression, in this case LABEL ~ x^2 for example, where LABEL is the string you want to assign from the vector labNames. bquote evaluates R code within the expression wrapped in .( ) and subsitutes the result into the expression.

Here is an example:

labNames <- c('xLab','yLab')
xlab <- bquote(.(labNames[1]) ~ x^2)
ylab <- bquote(.(labNames[2]) ~ y^2)
plot(c(1:10), xlab = xlab, ylab = ylab)

(Note the ~ just adds a bit of spacing, if you don't want the space, replace it with * and the two parts of the expression will be juxtaposed.)

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