How to give color to each class in scatter plot in R?

Question

In a dataset, I want to take two attributes and create supervised scatter plot. Does anyone know how to give different color to each class ?

I am trying to use col == c("red","blue","yellow") in the plot command but not sure if it is right as if I include one more color, that color also comes in the scatter plot even though I have only 3 classes.

Thanks

Answer 1

Here is an example that I built based on this page.

library(e1071); library(ggplot2)  mysvm      <- svm(Species ~ ., iris) Predicted  <- predict(mysvm, iris)  mydf = cbind(iris, Predicted) qplot(Petal.Length, Petal.Width, colour = Species, shape = Predicted,     data = iris) 

This gives you the output. You can easily spot the misclassified species from this figure.

Answer 2

Here is a solution using traditional graphics (and Dirk's data):

> DF <- data.frame(x=1:10, y=rnorm(10)+5, z=sample(letters[1:3], 10, replace=TRUE))  > DF     x        y z 1   1 6.628380 c 2   2 6.403279 b 3   3 6.708716 a 4   4 7.011677 c 5   5 6.363794 a 6   6 5.912945 b 7   7 2.996335 a 8   8 5.242786 c 9   9 4.455582 c 10 10 4.362427 a > attach(DF); plot(x, y, col=c("red","blue","green")[z]); detach(DF) 

This relies on the fact that DF$z is a factor, so when subsetting by it, its values will be treated as integers. So the elements of the color vector will vary with z as follows:

> c("red","blue","green")[DF$z]  [1] "green" "blue"  "red"   "green" "red"   "blue"  "red"   "green" "green" "red"     

You can add a legend using the legend function:

legend(x="topright", legend = levels(DF$z), col=c("red","blue","green"), pch=1)