R help - Aug 2006 - Colour-coding intervals on a line

Hi,
 
This is a simple version of something that I am trying to do. If I can
sort the problem basically, I figure I should be able to sort it for the
program I'm writing (which would take longer to explain).
 
I need to know if there is any way of using different colours for
different intervals of a line on a graph. Eg. If I plot the line y=x for
x=1:10, and split this line into 106 intervals (i.e. not a 'nice' number
of intervals) how could I colour different intervals different colours
without having to use segments and specify coordinates to join?
 
Thanks in advance for any help!
 
Sara-Jane

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Sara-Jane Dunn a ?crit :
> I need to know if there is any way of using different colours for
> different intervals of a line on a graph. Eg. If I plot the line y=x for
> x=1:10, and split this line into 106 intervals (i.e. not a 'nice'
number
> of intervals) how could I colour different intervals different colours
> without having to use segments and specify coordinates to join?
> Thanks in advance for any help!
> Sara-Jane
I think you'll have to use segments (?lines())
but it shouldn't be too complicated.

Put your line begin, line end, line color in a matrix(, ncol=106)
and call lines(...) in a for loop.

I would be happy to hear about another way to do it ?

Sara-Jane Dunn wrote:
> Hi,
>  
> This is a simple version of something that I am trying to do. If I can
> sort the problem basically, I figure I should be able to sort it for the
> program I'm writing (which would take longer to explain).
>  
> I need to know if there is any way of using different colours for
> different intervals of a line on a graph. Eg. If I plot the line y=x for
> x=1:10, and split this line into 106 intervals (i.e. not a 'nice'
number
> of intervals) how could I colour different intervals different colours
> without having to use segments and specify coordinates to join?
>  
Hi Sara-Jane,
This is a problem that I have been facing myself. I wanted to display 
color-coded curves that indicated something depending upon the values 
plotted. This might be useful to you, although you will need the 
functions color.scale and rescale from the plotrix package to make it work.

color.scale.lines<-function(x,y,redrange,greenrange,bluerange,
  scale.to="y",...) {

  lenx<-length(x)
  leny<-length(y)
  nseg<-lenx-1
  if(lenx != leny) {
   warning("x and y are different lengths - some values will be
ignored")
   if(lenx>leny) nseg<-leny-1
  }
  if(scale.to=="y")
   lcol<-color.scale(y[1:nseg],redrange,greenrange,bluerange)
  else lcol<-color.scale(x[1:nseg],redrange,greenrange,bluerange)
  segments(x[1:nseg],y[1:nseg],x[2:(nseg+1)],y[2:(nseg+1)],col=lcol,...)
}

plot(0,xlim=c(0,pi),ylim=c(0,1),type="n")
x<-seq(0,pi,length=106)
color.scale.lines(x,sin(x)*10,c(0,1),c(1,0),0,lwd=2)

Jim