Multiple ROC curves in one plot ROCR

Question

Is it possible to plot the roc curve for diffrent classifiers in the same plot using the ROCR package? I\'ve tried:

>plot(perf.neuralNet, colorize=TRUE)
>li         


        

Answer 1

The problem with your lines-approach is that there is no generic S4 lines function for an object of class performance defined in the ROCR package. But you can use the generic plot function as you did with an additional add = TRUE argument. For example this is partly from the example page of ?plot.performance:

library(ROCR)
data(ROCR.simple)
pred <- prediction( ROCR.simple$predictions, ROCR.simple$labels )
pred2 <- prediction(abs(ROCR.simple$predictions + 
                        rnorm(length(ROCR.simple$predictions), 0, 0.1)), 
        ROCR.simple$labels)
perf <- performance( pred, "tpr", "fpr" )
perf2 <- performance(pred2, "tpr", "fpr")
plot( perf, colorize = TRUE)
plot(perf2, add = TRUE, colorize = TRUE)

OR, you can store all your predictions in a matrix and do all the subsequent steps in one:

preds <- cbind(p1 = ROCR.simple$predictions, 
                p2 = abs(ROCR.simple$predictions + 
                rnorm(length(ROCR.simple$predictions), 0, 0.1)))

pred.mat <- prediction(preds, labels = matrix(ROCR.simple$labels, 
                nrow = length(ROCR.simple$labels), ncol = 2) )

perf.mat <- performance(pred.mat, "tpr", "fpr")
plot(perf.mat, colorize = TRUE)

Btw, if you for some reason really wanted to use lines to plot consecutive ROC curves you would have to do sth. like this:

plot(perf) 
lines(perf2@x.values[[1]], perf2@y.values[[1]], col = 2)