Highlight cells in heatmap

Question

I am currently trying to set up a heatmap of a matrix and highlight specific cells, based on two other matrices.

An example:

> SOI
         NAP_G0         


        

Answer 1

When add.expr is called the plot is set so that the centre of the cells is at unit integer values. Try add.expr=points(1:5,1:5) to see. Now all you need to do is write a function that draws boxes (help(rect)) with the colours you need, at the half-integer coordinates.

Try this:

set.seed(310366)

nx=5
ny=6
SOI=matrix(rnorm(nx*ny,100,50),nx,ny)

colnames(SOI)=paste("NAP_G0",sort(as.integer(runif(ny,10,99))),sep="")
rownames(SOI)=sample(2315101:(2315101+nx-1))
above150 = SOI>150
below30=SOI<30

makeRects <- function(tfMat,border){
  cAbove = expand.grid(1:nx,1:ny)[tfMat,]
  xl=cAbove[,1]-0.49
  yb=cAbove[,2]-0.49
  xr=cAbove[,1]+0.49
  yt=cAbove[,2]+0.49
  rect(xl,yb,xr,yt,border=border,lwd=3)
}

heatmap(t(SOI),Rowv = NA, Colv=NA, add.expr = {
 makeRects(above150,"red");makeRects(below30,"blue")})