Unicode symbols in R

A friend asked me this morning if there was a way to plot a symbol in R (as a plotting character) representing a half-filled circle. I didn't know, but I figured this out (perhaps it's demonstrated elsewhere -- the ability to use Unicode symbols was added in 2008 or so -- but I didn't stumble across it). First, looking at this list of Unicode shapes indicated that I wanted Unicode symbol 25D1. Then looking at ?points indicated that I could use a negative value (in this case -0x25D1L allows me to enter the value as hexadecimal: the L denotes a (long) integer). So

plot(1,1,pch=-0x25D1L)
plot(1,1,pch=-as.hexmode("25D1"))
plot(1,1,pch=-0x25D1L)

all work equivalently.

TestUnicode <- function(start="25a0", end="25ff", ...)
  {
    nstart <- as.hexmode(start)
    nend <- as.hexmode(end)
    r <- nstart:nend
    s <- ceiling(sqrt(length(r)))
    par(pty="s")
    plot(c(-1,(s)), c(-1,(s)), type="n", xlab="", ylab="",
         xaxs="i", yaxs="i")
    grid(s+1, s+1, lty=1)
    for(i in seq(r)) {
      try(points(i%%s, i%/%s, pch=-1*r[i],...))
    }
  }

TestUnicode()
TestUnicode(9500,9900)  ## some cool spooky stuff in here!

One thing to keep in mind is that you should test whatever symbols you decide to use carefully with whatever graphics path/display/printing solution you plan to use, as all platforms may not render all Unicode symbols properly. With a little more work I could change TestUnicode() to do proper indexing so that it would be easier to figure out which symbol was which. Watch for my next paper, in which I will use Unicode symbols 9748/x2614 ('UMBRELLA WITH RAIN DROPS'), 9749/x2615 ('HOT BEVERAGE'), 9763/x2623 ('BIOHAZARD SIGN'), and 9764/x2624 ('CADUCEUS') to represent my data ... Related links:

• Unicode symbol search
• Yu-Sung Su on plotting symbols
• Yihui Xe on using tikZ to embed TeX symbols in R graphics

PS This worked fine on my primary 'machine' (Ubuntu 10.04 under VMWare on MacOS X.6), but under MacOS X.6 most of the symbols were not resolved. The friend for whom I worked this out has also stated that it didn't work under his (unstated) Linux distribution ... feel free to post in comments below if this works on your particular machine/OS combination. There is a remote possibility that this could be done with Hershey fonts as well (see this page on the R wiki for further attempts at symbol plotting), but I don't know how thorough the correspondence is between the Hershey fonts and the Unicode symbol set ...

PPS I asked about this on StackOverflow and got a useful answer from Gavin Simpson, referencing some notes by Paul Murrell: use cairo_pdf. This should work on any Linux installation with the Pango libraries, I think. In principle it could work on MacOS (and/or Windows?) with Pango installed as well, but I haven't tried ...