Q:

x-axis in boxplot in R

I hope that with this edition my question improve and it could be reproducible.
Imagine I have this data, in which X are certain values of a measure and Y are 4 groups, each one representing forage quality. I could used letters for the forage quality, as L (low), M (medium), H (high) and VH (very high), but I use the values because I want the boxplots to be drawn in the x-axis at this real points, 4.8, 13, 18.02 and 21, and not with the same distance between them. 
    Data <- data.frame(X = sample(1:12),
    Y = sample(rep(c(4.8, 13, 18.02, 21), each=3)))

I use this simple code to draw the boxplot
    boxplot(Data$X ~ Data$Y)

How could I scale the boxplots along the x-axis? Should I use any graphic library instead?
Thanks

A:

You want to use the at argument to boxplot to specify where the boxes are drawn. Specifically:
boxplot(Data$X ~ Data$Y, at = sort(unique(Data$Y)))

