plot axis labels with multiple colours

Question

I'm making plots like the one generated with the following code:

var1 <- sort(runif(10, 0, 1), decreasing = TRUE)
var2 <- sort(runif(10, 0, 1))
plot(var1, pch = 20, ylab = c("Var 1", "Var 2"))
points(var2, pch = 20, col = "grey")

Is there a way, with just the R graphics package, to place a black circle before Var 1 and a grey circle before Var 2 in the y axis label, to avoid having to insert a legend? Or alternatively, a way to use different text colours (black for Var 1 and grey for Var 2) in the y axis? I tried using col.lab = c("black","grey"), but it says Error in plot.window(...) : graphical parameter "col.lab" has the wrong length.

Many thanks in advance,

Márcia

Answer 1

I'm not sure how to add the point to the label, but an easy way to labe with color can be done in the following way:

var1 <- sort(runif(10, 0, 1), decreasing = TRUE)
var2 <- sort(runif(10, 0, 1))
plot(var1, pch = 20, ylab = "")
points(var2, pch = 20, col = "grey")
mtext("Var 1", side=2, line=2)
mtext("Var 2", side=2, line=3, col="grey")

Answer 2

Would something like this work for you? It's a bit busy on the left axis, but I think it shows what you are asking about.

> var1 <- sort(runif(10, 0, 1), decreasing = TRUE)
> var2 <- sort(runif(10, 0, 1))
> plot(var1, ylim = range(c(var1, var2)), pch = 20, ylab = "", axes = FALSE)
> points(var2, pch = 20, col = "grey")
> labs <- round(sort(c(var1, var2)), 1)
> axis(1)
> axis(2, at = sort(c(var1, var2)), labels = labs)
> sapply(var1, function(x) points(-0.1, x, pch = 20))
> sapply(var2, function(x) points(-0.1, x, pch = 20, col = "grey"))
> box()