Question

I am looking for a way to plot a matrix of type character:

m=matrix(data=c("A","A","B","B","B","C","C","B"),nrow=4,ncol=2)
> m
     [,1] [,2]
[1,] "A"  "B" 
[2,] "A"  "C" 
[3,] "B"  "C" 
[4,] "B"  "B" 

with a defined set of colours

A="Yellow"
B="Blue"
C="Green"

Should I pass from matrix to ascii and use image() from sp package?

I am looking fro something like this:

Answer 1

It rather depends on what you meant by “plot a matrix”:

 m2 <- m
 m2[] <- c("yellow", "blue","green")[match(m, c("A","B","C"))]
 m2
#------------
 [,1]     [,2]   
[1,] "yellow" "blue" 
[2,] "yellow" "green"
[3,] "blue"   "green"
[4,] "blue"   "blue" 
#------------
plot(row(m2), col(m2), col=m2, pch=18, cex=4)

This plots solid diamonds of the specified color at the matrix locations determined by the row and columns of matrix m. Another way with image:

m2[] <- match(m, c("A","B","C"))
mode(m2) <- "numeric"
m2
image(1:nrow(m2), 1:ncol(m2), m2, col=c("yellow", "blue","green"))