image function in R

Question

I'm trying to do something a little bit complicated for a beginner in programming. I have a matrix 16x16 and I want to plot the values as a heatmap using image() in R. How can I plot the "0" (zeros) in blue when the sum (row index + column index) is <= 15? Is that possible?

example matrix:

x <-  c(3045, 893, 692, 830, 617, 155, 246, 657, 105, 60, 18, 7, 7, 4, 2, 11234, 
2985, 2242, 2471, 1575, 366, 503, 1283, 170, 79, 32, 6, 4, 1, 3, 19475, 4756, 
3233, 3251, 1810, 409, 575, 1210, 139, 41, 11, 4, 2, 0, 0, 20830, 4739, 2990, 
2531, 1346, 298, 325, 612, 60, 17, 1, 0, 1, 0, 0, 15304, 3196, 1885, 1440, 610, 
117, 115, 185, 14, 2, 0, 0, 0, 0, 0, 8026, 1535, 806, 539, 223, 33, 37, 39, 0, 
0, 0, 0, 0, 0, 0, 3300, 562, 286, 141, 45, 14, 5, 12, 0, 0, 0, 0, 0, 0, 0, 1067, 
160, 65, 40, 14, 1, 2, 0, 0, 0, 0, 0, 0, 0, 0, 277, 47, 6, 2, 1, 0, 1, 0, 0, 0, 
0, 0, 0, 0, 0, 72, 6, 1, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 11, 5, 0, 0, 0, 0, 
0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0)

xmat <- matrix(x, ncol = 12)
xmat <- cbind(xmat, rep(0,16), rep(0,16), rep(0,16), rep(0,16))
xmat <- rbind(xmat, rep(0,16))
dimnames(xmat) = list(0:15, 0:15)
xmat

Thanks! Vitor

Answer 1

Plot the cases meeting the criteria as blue.

xmat.new <- xmat
xmat.new[!((row(xmat) + col(xmat) <= 15) & xmat==0)] <- NA
image(xmat.new,col="blue")

Plot the cases not meeting the criteria as normal. Notice the add=TRUE

xmat.new <- xmat
xmat.new[((row(xmat) + col(xmat) <= 15) & xmat==0)] <- NA
image(xmat.new,add=TRUE)

Result:

Edited to include @Marek's suggestion to simplify the statements.