[EMAIL PROTECTED] wrote:
Dear wonderful R community,

I've been creating color-coded concentric circles using the "points" function, but I just realized that what I would really like to do is draw color-coded concentric half-circles.

What should I do?

Write a 'halfCircle' function.

halfCircle <- function(x,y,r,start=0,end=pi,nsteps=30,...){
  rs <- seq(start,end,len=nsteps)
  xc <- x+r*cos(rs)
  yc <- y+r*sin(rs)
  lines(xc,yc,...)
}

Then try it out:

plot(1:10)

# default draws top halves:
halfCircle(5,5,2)
halfCircle(6,6,1,col="red")

# draw right half:
halfCircle(5,4,1,start=-pi/2,end=pi/2,lwd=2,col="blue")

Note that you'll have to call halfCircle once for each point, since its not 'vectorised' in any way.

It's also capable of drawing any circle fragments. I should have called it 'partCircle'. Oh well.

Barry

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