How to only make one legend name italic in base R

Question

I want to add a legend to a plot in which only one of the legend names is italicized. I'm using plot() in base R.

• However, I need that italicized line to contain variable numbers, so I use bquote.

What I've tried does not work:

  a <- 2 ; b <- 5
  plot(a,b)
  l1 <- bquote(Italic ~ .(a) + .(b))
  l2 <- bquote(a + b)
  legend(x='topright',legend = bquote(italic(.(l1))))
  legend(x='topleft',legend = c(bquote(italic(.(l1))),l2))

• Notice that when I leave the expression on its own (RIGHT LEGEND), it italicizes correctly. However, when I add the text for other legend lines, it messes up (LEFT LEGEND).

How do I properly do this?

^{Note: I'd rather have a solution that doesn't require multiple calls to legend().}

Answer 1

You should use as.expression to coerce everything into an expression object.

a <- 2
b <- 5
plot(a,b)
legend("topleft", legend = c(as.expression(bquote(italic("Italic: "*.(a)*" + "*.(b)))),
    as.expression(bquote("Non Italic: "*.(a)*" + "*.(b)))) )

To modify your example

a <- 2
b <- 5
plot(a,b)
l1 <- bquote(Italic ~ .(a) + .(b))
l2 <- bquote(a + b)
legend("topleft", legend =  c(as.expression(bquote(italic(.(l1)))),
                            as.expression(bquote(.(l2))) ))

Answer 2

You could use text.font = 3, say:

legend(x='topleft',legend = c(bquote((.(l1))),l2), text.font=c(3,1))