Pie Slices: Circle Segments for Pie Charts With Different Radii in R

Question

I want to create a different kind of pie chart, in which I can specify not only the percent that goes to each segment (x \in [0,1]), but also how far each pie segment's radius extends out. (The idea is to display a second dimension which is the product of the x and some other variable.) I also need to fill and label the segments. This would be easiest if the function did the labeling itself or returned the mid point of each segment's outer arc.

(If no one has written this, the primitive function that I need is a filled circle segment with center x,y extending to radius r from angle a1 to a2. draw.arc() from plotrix looked good, but col does not fill [it sets only the outer color].)

Do such function(s) already exist or do I need to write it myself? Pointers appreciated.

Check this question: https://stackoverflow.com/questions/33343463/how-to-use-r-to-plot-a-pie-plot-with-different-radius — Lamia, Oct 23 '20 at 21:34
thanks, I did (apologies--I should have mentioned it), but it did not answer it. it seems to be a very special kind of radial plot, not readily generalizable. — ivo Welch, Oct 24 '20 at 03:31

score 1 · Answer 1 · answered Oct 26 '20 at 00:11

pie.slice <- function( center, radius, arc1, arc2, ..., fine=1, label=NULL, label.dist=1 ) {
    stopifnot( length(arc1) == 1 )
    stopifnot( length(arc2) == 1 )
    stopifnot( (arc1 >= 0.0) & (arc1 <= 1.0) )
    stopifnot( (arc2 >= 0.0) & (arc2 <= 1.0) )
    stopifnot( arc2 > arc1 )
    stopifnot( length(center) == 2)
    stopifnot( length(radius) <= 2)
    if (length(radius)==1) radius <- c(radius,radius)

    xb <- seq(arc1, arc2, length.out= (arc2 * 180 - arc1 * 180) * fine)

    x <- center[1] + c( 0, cospi(2*xb), 0 )*radius[1]
    y <- center[2] + c( 0, sinpi(2*xb), 0 )*radius[2]

    polygon( x, y, ... )

    mid <- (arc1 + arc2)/2
    anchor <- c( center[1] + cospi(2*mid )*radius[1], center[2] + sinpi(2*mid)*radius[2] )

    if (!is.null(label))
        text( anchor[1], anchor[2], label, adj=c(-0.5,1.0 )*label.dist, srt= mid*360 )

    anchor  ## returns the anchor point halfway for your own text drawing
}

For demonstration,

pdf("pieslice.pdf", width=12, height=12, pointsize=12/0.75)
plot( 0, xlim=c(-1,2), ylim=c(-1,2), xlab="", ylab="", type="n" )

radius <- 0.04
sl.out <-seq(0.0, 1.0, 0.1)

my.center <- c(-0.25,1)
for (i in 2:(length(sl.out)-1))
    pie.slice( my.center, radius*i,  sl.out[i-1], sl.out[i], label=LETTERS[i], density=i*2 )

my.center <- c(1.0,0.0)
for (i in 2:length(sl.out))
    pie.slice( my.center, 1.5*radius*(length(sl.out)-i+1), sl.out[i-1], sl.out[i],
              label=paste("from ", sl.out[i-1], " to ", sl.out[i]), col=i, label.dist=0.25 )

dev.off()

to obtain a figure like

Pie Slices: Circle Segments for Pie Charts With Different Radii in R

1 Answers1