I want to get the actual value of the points in the circle.
Can you tell me how to get them?
Thanks!

> insiders
 [1] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
[13] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
[25] FALSE FALSE FALSE FALSE FALSE  TRUE  TRUE FALSE FALSE FALSE FALSE FALSE
[37] FALSE FALSE FALSE FALSE FALSE  TRUE FALSE  TRUE FALSE FALSE  TRUE FALSE
[49] FALSE  TRUE



On 4/22/06, Gabor Csardi <csardi@rmki.kfki.hu> wrote:
>
> Fine, than just check every point like suggested below.
> (whether (c1-x)^2+(c2-y)^2 < r^2)
> and call 'symbols' to add the circle to the plot like this:
> symbols(c1, c2, circles=r, inches=FALSE, add=TRUE)
>
> For example, if coords is a two column matrix of the coordinates of the
> points:
>
> ################################
> coords <- matrix( runif(100), nc=2 )
> c1 <- c2 <- 0.5
> r <- 0.2
>
> insiders <- apply(coords, 1,
>                   function(co) (c1-co[1])^2+(c2-co[2])^2 < r^2)
> plot(coords)
> symbols(c1, c2, circles=r, inches=FALSE, add=TRUE)
> ################################
>
> 'insiders' will be a logical vector telling whether the points are inside
> or
> outside the circle.
>
> Gabor
>
> On Sat, Apr 22, 2006 at 02:16:38PM -0400, Jian Zhang wrote:
> > Thanks!
> > There are many points in our plot. I want to choose the points which
> > distance to one point (e.g.(100,200)) is less than 10.
> > And I want to draw a circle (radinus=10). The centre of the circle is
> the
> > point (100,200).
> >
> >
> > On 4/22/06, Gabor Csardi <csardi@rmki.kfki.hu> wrote:
> > >
> > >Hmmm, could you explain this a bit?
> > >You want to add a circle to a plot? See the examples in help(symbols)
> > >
> > >Or you want to calculate the coordinates of the points on a circle?
> > >
> > >t <- seq(0,2*pi,length=100)
> > >coords <- t(rbind( 10+sin(t)*2, 20+cos(t)*2))
> > >plot(coords)
> > >
> > >Here (10,20) is the center of the circle, and 2 is its radius.
> > >If you set length to a bigger number you'll get smoother resolution.
> > >
> > >A points (x,y) is inside the circle if (c1-x)^2+(c2-y)^2 < r^2
> > >(c1, c2) is the center of the circle, r is its radius.
> > >
> > >Gabor
> > >
> > >On Sat, Apr 22, 2006 at 01:42:46PM -0400, Jian Zhang wrote:
> > >> how to draw a circle (e.g. radius=10cm) of one point?
> > >> And how to choose these points in the circle?
> > >> Thanks!
> > >>
> > >>       [[alternative HTML version deleted]]
> > >>
> > >> ______________________________________________
> > >> R-help@stat.math.ethz.ch mailing list
> > >> https://stat.ethz.ch/mailman/listinfo/r-help
> > >> PLEASE do read the posting guide!
> > >http://www.R-project.org/posting-guide.html
> > >
> > >--
> > >Csardi Gabor <csardi@rmki.kfki.hu>    MTA RMKI, ELTE TTK
> > >
>
> --
> Csardi Gabor <csardi@rmki.kfki.hu>    MTA RMKI, ELTE TTK
>
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