[R] Help with color coded bar graph

[Marc Schwartz]

On Fri, 2007-09-07 at 15:07 -0500, Marc Schwartz wrote:
> On Fri, 2007-09-07 at 12:45 -0700, Luis Naver wrote:
> > I have a list of observations that are -1, 1 or 0.  I would like to  
> > represent them in a horizontal bar color coded based on value like a  
> > stacked bar graph. I can achieve this in the form of a png with the  
> > following code:
> > 
> > A = floor(runif(10)*3) - 1
> > 
> > png(width=100, height=10)
> > par(mar=c(0,0,0,0))
> > image(matrix(A), col=grey(c(0.1, 0.5, 0.9)))
> > dev.off()
> > 
> > However I would like to do this with one of the standard plotting  
> > tools (i.e. barplot) to take advantage of labels and multiple  
> > series.  Any help would be appreciated.
> > 
> > - Luis Naver
> 
> How about this:
> 
>   barplot(rep(1, length(A)), col = "black", space = 0, border = 0)
> 
>   barplot(A, col = grey(0.9), space = 0, border = 0, add = TRUE)
> 
> The first call sets the plot region to black, ensuring that the x and y
> axes are consistent with the second call.
> 
> Alternatively, you can use barplot2() in the gplots CRAN package to do
> this in a single call, as it has an argument to color the plot region.

Actually, here is an easier way:

barplot(rep(1, length(A)), 
        col = ifelse(A == 0, "black", grey(0.9)), space = 0, border = 0)

Just set 'col' based upon the value in 'A'.

HTH,

Marc