set.seed(31)
y <- matrix(rnorm(50),
            10,
            5,
            dimnames=list(paste("g", 1:10, sep=""),
                          paste("t", 1:5, sep=""))
            )
 
# data needs to be in long format
# install reshape if necessary
#install.packages("reshape")
library(reshape)
yy <- melt(y)
 
ggplot(yy, aes(x=X1, y=X2, fill=value)) +
  geom_raster() +
  scale_fill_gradient2(midpoint=0, mid="grey70", limits=c(-2,2))

ctc

ctc

heatmap(...) function can draw a heatmap, it's usage is:

heatmap(x, Rowv=NULL, Colv=if(symm)"Rowv" else NULL,
        distfun = dist, hclustfun = hclust,
        reorderfun = function(d,w) reorder(d,w),
        add.expr, symm = FALSE, revC = identical(Colv, "Rowv"),
        scale=c("row", "column", "none"), na.rm = TRUE,
        margins = c(5, 5), ColSideColors, RowSideColors,
        cexRow = 0.2 + 1/log10(nr), cexCol = 0.2 + 1/log10(nc),
        labRow = NULL, labCol = NULL, main = NULL,
        xlab = NULL, ylab = NULL,
        keep.dendro = FALSE, verbose = getOption("verbose"), ...)


x: Numeric matrix
Rowv: Row dendrogram
Colv: Column dendrogram