[R] Ploting different values with different colors

[Jim Lemon]

On 03/01/2013 10:54 AM, Benoit Gendreau-Berthiaume wrote:
> Hello I am  trying to plot a 20 x 20 grid of points with the colors of each
> point refering to percent cover of that specific point
>
> So basically the point are all the same size and their position on the
> graph is base on their coordinates (x,y). I want the color (a grey scale
> from white=0 to black =100) to represent the values of each of these point
> (cover)
>
> Here is what my data looks like
>          x     y           cover
> A1   0   95             3.0
> A2   5   95             0.5
> A3  10  95            10.0
> ...etc
> Up to now I have tried
> plot(Q.xy[,1],Q.xy[,2],pch=16, cex=2.6, col=heat.colors(8)[x[,3]])
> I put 8 after heat colors because their are 8 different values in my cover
> column
>
> My problem is that I only get one color out this line of code. Regardless
> of which number I put after heat.colors I always have the same quadrats
> colored with only one color.
>
> Any idea of how to get 8 colors in my graph?
> and how to make sure they are associated with the good cover values?
>
Hi Benoit,
This can be done with a number of R functions. I will shamelessly 
demonstrate one that I wrote myself:

Q<-data.frame(x=sample(0:100,20),y=sample(0:100,20),
  cover=runif(20,0,100))
library(plotrix)
Qcolors<-color.scale(Q$cover,extremes=c("white","black"),
  xrange=c(0,100))
plot(Q$x,Q$y,pch=21,col="black",bg=Qcolors,cex=2)

Jim