Colouring plot by factor in R

Question

I am making a scatter plot of two variables and would like to colour the points by a factor variable. Here is some reproducible code:

data <- iris plot(data$Sepal.Length, data$Sepal.Width, col=data$Species) 

This is all well and good but how do I know what factor has been coloured what colour??

Answer 1

data<-iris plot(data$Sepal.Length, data$Sepal.Width, col=data$Species) legend(7,4.3,unique(data$Species),col=1:length(data$Species),pch=1) 

should do it for you. But I prefer ggplot2 and would suggest that for better graphics in R.

Answer 2

The command palette tells you the colours and their order when col = somefactor. It can also be used to set the colours as well.

palette() [1] "black"   "red"     "green3"  "blue"    "cyan"    "magenta" "yellow"  "gray"    

In order to see that in your graph you could use a legend.

legend('topright', legend = levels(iris$Species), col = 1:3, cex = 0.8, pch = 1) 

You'll notice that I only specified the new colours with 3 numbers. This will work like using a factor. I could have used the factor originally used to colour the points as well. This would make everything logically flow together... but I just wanted to show you can use a variety of things.

You could also be specific about the colours. Try ?rainbow for starters and go from there. You can specify your own or have R do it for you. As long as you use the same method for each you're OK.