[R] Transparent Pie Charts

[Uwe Ligges]

Werner Wernersen wrote:
> Hi again!
> 
> I put this question in another topics post before but
> I fear it might drown there.
> 
> Is it possible to have transparent / alpha blended
> colors for pie charts?
> I am using the pies in a map of pies and those pies
> are sometimes overlapping so 
> it would be great to see if another pie lies beneath.
> 
> Thanks,
>    Werner
> 
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You have already found Paul Murrell's R News 3(2) article. You might 
also want to take a look at the page of his forthcoming book: 
http://www.stat.auckland.ac.nz/~paul/RGraphics/rgraphics.html

For transparency/alpha blending see the article "Fonts, Lines and 
Transparency in R Graphics" in the latest R News 4(2). Transparency 
works on many devices, alpha blending only on a few (pdf, for example).

Let's change Paul's code from R News 3(2) to allow transparency:


   x <- c(0.88, 1, 0.67, 0.34)
   y <- c(0.5, 0.4, 0.6, 0.55)
   set.seed(1234)
   z <- matrix(runif(4 * 2), ncol = 2)
   oldpar <- par(no.readonly = TRUE)
   plot(x, y, xlim = c(-0.2, 1.2), ylim = c(-0.2, 1.2), type = "n")
   vps <- baseViewports()
   par(new = TRUE)
   pushViewport(vps$inner, vps$figure, vps$plot)
   grid.segments(x0 = unit(c(rep(0, 4), x), rep(c("npc", "native"),
                           each = 4)),
                 x1 = unit(c(x, x), rep("native", 8)),
                 y0 = unit(c(y, rep(0, 4)), rep(c("native", "npc"),
                           each = 4)),
                 y1 = unit(c(y, y), rep("native", 8)),
                 gp = gpar(lty = "dashed", col = "grey"))
   maxpiesize <- unit(1, "inches")
   totals <- rowSums(z)
   sizemult <- totals/max(totals)
   for (i in 1:4) {
     pushViewport(viewport(x = unit(x[i], "native"),
                           y = unit(y[i], "native"),
                           width = sizemult[i] * maxpiesize,
                           height = sizemult[i] * maxpiesize))
     grid.rect(gp = gpar(col = "grey", lty = "dashed"))
     par(plt = gridPLT(), new = TRUE)
     pie(z[i, ], radius = 1, labels = rep("", 2),
         col = c("transparent", "lightblue"))
     popViewport()
   }
   popViewport(3)
   par(oldpar)




Uwe Ligges