Question

How can I warp the default rainbow in R. For instance, take a look at this code and the image it produces:

x = seq(0,50,by=0.005)
y = runif(length(x),2,5)
colors = rainbow(length(x))
plot(x,y,cex=0.2,pch=16,col=colors)

I want to alter this so that there is not so much green. There should be as much green as there is yellow and cyan and blue. I also want to remove magenta (the “redish” color on the far right). How could I go about doing this?

Answer 1

If you skip green explicitly out of the palette generation, you get close to what you want I think:

par(mfrow=c(2,1))
par(mar=c(2,1,3,1))

x = seq(0,50,by=0.005)
y = runif(length(x),2,5)
colors = rainbow(length(x))
plot(x,y,cex=0.2,pch=16,col=colors)
title(main="old")

crp.rg <- colorRampPalette(c("red","yellow","cyan","blue","red"))
colors = crp.rg(length(x))
plot(x,y,cex=0.2,pch=16,col=colors)
title(main="new")

edit

You could also manually edit each colour transition to make them a different length:

par(mfrow=c(2,1))
par(mar=c(2,1,3,1))

x = seq(0,50,by=0.005)
y = runif(length(x),2,5)
colors = rainbow(length(x))
plot(x,y,cex=0.2,pch=16,col=colors)
title(main="old")


crp.step1 <- colorRampPalette(c("red","yellow"))
crp.step2 <- colorRampPalette(c("yellow","green"))
crp.step3 <- colorRampPalette(c("green","cyan"))
crp.step4 <- colorRampPalette(c("cyan","blue"))
crp.step5 <- colorRampPalette(c("blue","red"))

colors <-   c(
           crp.step1(2666),
           crp.step2(1000),
           crp.step3(1000),
           crp.step4(2666),
           crp.step5(2667)
        )

plot(x,y,cex=0.2,pch=16,col=colors)
title(main="new")