Cross tabulation plot with numbers in R

Question

I would like to add the frequency numbers of each combination on a cross-tabulation plot.

For example, with the mtcars example:

data("mtcars")
table(mtcars$vs, mtcars$am)

We have the number of each combination between $vs and $am columns. If I directly plot this, I get 4 rectanges which size vary based on the frequency numbers:

plot(table(mtcars$vs, mtcars$am), main = "Cross tabulation plot",
     xlab = "Engine (vs)", ylab = "Transmission (am)")

Would it be possible to print these frequency numbers within the corresponding rectangle in an elegant way?

Answer 1

In this way you can show a number in each square. Basically the idea is to calculate the position of the numbers so that they will fit the center of the square.

tbl <- table(mtcars$vs, mtcars$am)
prpX <- prop.table(table(mtcars$vs))
prpY <- prop.table(table(mtcars$vs, mtcars$am), margin = 1)

plot(tbl, main = "Cross tabulation plot",
     xlab = "Engine (vs)", ylab = "Transmission (am)")
text(prpX/2 * c(1,-1) + 0:1,
     prpY/2 * c(-1,-1,1,1) + c(1,1,0,0),
     tbl)