Dear all,
I want some help improve my ggplot as following:
Make the plottable area with grid, so is easy one to see where each box refers to x and y values.
Add a color bar but with fixed values, that I want to specify.
How   I can do those two?

Before is some code what I have tried so far.

Regards
Alex 


DataToPlot<-matrix(data=seq(1:9),nrow=3,dimnames=list(seq(1,3),seq(4,6)))                       


require(reshape)
require(ggplot2)
require(raster)
                                                                                                                                                                                                                                             
 tdm <- melt(DataToPlot)              



p<- ggplot(tdm, aes(x = Var2, y = Var1, fill = factor(value))) +
            labs(x = "MHz", y = "Threshold", fill = "Duty Cycle") +
            geom_raster() +
            scale_fill_discrete()

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