colorRampPalette_with_zeropoint

# Author: Jakob Richter (https://gist.github.com/jakob-r)
# colfuncMiddle does the same as colfunc but gives respect to middle point.
# usage: x : numeric() 
#        colfunc: function generated by colorRampPalette()
#        zeropoint: numeric(1)

colfuncMiddle = function(x, colfunc, n, zeropoint=0){
  stopifnot(is.numeric(x) | is.factor(x))
  if(!missing(n)){
    stopifnot(length(n)==1)
    stopifnot(n>0)
  }
  if(is.factor(x)) {
    n = length(levels(x))
    x = as.numeric(x)
  }
  givenRange = range(x, na.rm=TRUE)
  neededRange = c(-1,1) * max(abs(zeropoint-givenRange)) + zeropoint
  neededBreaks = ceiling(diff(neededRange)/diff(givenRange) * n)
  myPalette = colfunc(n=neededBreaks)
  if((neededRange - givenRange)[1]==0){
    myPalette = head(myPalette, n)
  }else{
    myPalette = tail(myPalette, n)
  }
  myPalette
}

# # Example:
# nbreaks = 10
# zeropoint = 0
# colfunc = colorRampPalette(c("green","white","red"),  space = c("Lab"))
# x = runif(100,min=-5,max=10)
# myPalette = colfuncMiddle(x, colfunc, nbreaks, zeropoint)
# cutted = cut(x, breaks=nbreaks)
# barplot(table(cutted), col=myPalette)