Using plotmath for graph labels.

(Here’s the “.Rmd” file that produced what you’re reading: label.Rmd.)

Here are several plots with successively harder labels using text, the value of a variable, and plotmath notation.

First, an easy text title:

curve(sqrt(x), from=0, to=4, main="Ugly plain text: y = sqrt(x)")

Second, an easy title using plotmath and bquote, but no text:

curve(sqrt(x), from=0, to=4, main=bquote(sqrt(x)))

Third, combine plotmath and text:

• In the context of “bquote()”, the asterisk, “*”, indicates joining

curve(sqrt(x), from=0, to=4, main=bquote("The square root of n: " * sqrt(n)))

Fourth, combine text and the value of a variable:

n = 2
curve(sqrt(x), from=0, to=4, main=paste(sep="", "The square root of ", n, " is ", sqrt(n)))

Fifth, combine plotmath and the value of a variable:

• In plotmath, sqrt(2) indicates \(\sqrt{2}\)
• bquote() facilitates plotmath and also allows the inclusion of the value of a variable:
  • “.()” indicates, in the context of “bquote()”, that its argument should be evaluated, so
    • “.(n)” indicates the value of the “n” variable, that is, 2
    • “.(sqrt(n))” indicates the value of “sqrt(n)”, that is, 1.414…
• here “bquote()” combines the previous two elements into a title

n = 2
curve(sqrt(x), from=0, to=4, main=bquote(sqrt(.(n))==.(sqrt(n))))

Sixth and finally, combine text, plotmath, and the value of a variable:

n = 2
curve(sqrt(x), from=0, to=4, main=bquote("The square root of " * .(n) * " is " * sqrt(.(n))==.(sqrt(n))))