[R] use same breaks and colors, but the displayed scale are different-image.plot()

[Jim Lemon]

On 09/16/2010 12:05 PM, rusers.sh wrote:
> Hi all,
>    I want to put several figures in a one figure for easy comparison, so i
> need to use the same methods to plot these figures. The following is an
> example. I also list my method, but it does not work.
> #Example data
> x<- 1:10; y<- 1:10; z<- outer( x,y,"+");z2<- outer( x,y,"-")
> #Quick view them
> image.plot(x,y,z)  #relatively larger value
> image.plot(x,y,z2)   #relatively small value
> #define the same breaks and colors
> brks<-quantile(c(as.vector(z),as.vector(z2)),na.rm=TRUE)
> colsn<-length(brks)-1
> cols<-gray((colsn:1)/colsn)
> #I expect they use the same breaks and colors
> par(mfrow=c(1,2))
> image.plot(x,y,z,breaks=brks,col=cols)
> image.plot(x,y,z2,breaks=brks,col=cols)
> par(mfrow=c(1,1))
>    I think they really use the same breaks and colors, but you can see the
> color legends are still different. One is 20-15-10-5, another is 5-0--5.
>    I hope they not only use the same breaks and colors, but also display the
> same color legends. How can i do it?

Hi Jane,
The color.legend function in the plotrix package will do this - see the 
examples, especially those for the "barp" function.

Jim