R: legend expression how to add comma between two values and how to supress scientific notation

Question

I'm trying to format the legend in my plot, but I have to use expression() because of greek and superscripts. However, when I want to display r^2 = 0.45, P<0.0001, I get r^2 = 0.45 P<1e-04, when I type in

legend(expression(r^2==0.9230~~P<0.0001))

I tried looking up the list() function but it doesn't help with the commas. I couldn't find anything on using decimals in the expression() function either.

Any suggestions would be appreciated.

Thanks

Answer 1

You can use paste() (within the call to expression()) to splice together character strings and unquoted expressions. The unquoted bits will be evaluated using the special rules exhibited by example(plotmath) and demo(plotmath), while the character strings will be printed verbatim.

Here's an example (which also uses phantom(), because the < operator expects/needs something to both its left and its right):

plot(1)
legend(x = "topleft", 
       legend = expression(paste(r^2==0.9230, ",  ", P<phantom(), "0.0001")))