[R] Drawing sample from a circle

[(Ted Harding)]

On 18-Jun-10 08:04:36, Ron Michael wrote:
> Hi, I would like to draw 10 uniformly distributed sample points from a
> circle with redius one and centered at (0,0). Is there any R function
> to do that?
> _
> Thanks,

You can quite easily write one.

[A]
Sampling uniformly on the circumference of the circle:

  csamp <- function(n,rad=1,centre=c(0,0)){
    x0 <- centre[1] ; y0 <- centre[2]
    u <- 2*pi*runif(n)
    rad*cbind(x=cos(u)+x0, y=sin(u)+y0)
  }

# Returns an nx2 matrix whose two columns are the x and y coordinates

[B]
Sampling uniformaly within the circle

  Csamp <- function(n,rad=1,centre=c(0,0)){
    x0 <- centre[1] ; y0 <- centre[2]
    u <- 2*pi*runif(n)
    r <- sqrt(runif(n))
    rad*cbind(x=r*cos(u)+x0, y=r*sin(u)+y0)
}

# Returns an nx2 matrix whose two columns are the x and y coordinates

[C]
Examples:

  plot(csamp(100),asp=1)

  plot(Csamp(1000),asp=1)

Ted.

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Date: 18-Jun-10                                       Time: 10:33:00
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