R：Plot 使用 ROCR 的多个不同颜色的 ROC 曲线

Question

The following code was taken from @adibender answer to "Multiple ROC curves in one plot ROCR". The code is partly from?plot.performance.

library(ROCR)
data(ROCR.simple)
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)

I want to illustrate several ROC curves in a single plot, like the code above, using the r package ROCR. However, i would want the ROC curves to be in different colours. How do i apply different colours to different curves? Thanks, in advance.

Answer 1

Try this (you can do it with ROCR ):

library(ROCR)
data(ROCR.simple)
preds <- cbind(p1 = ROCR.simple$predictions, 
               p2 = abs(ROCR.simple$predictions + 
                          rnorm(length(ROCR.simple$predictions), 0, 0.1)))
n <- 2 # you have n models
colors <- c('red', 'blue') # 2 colors
for (i in 1:n) {
   plot(performance(prediction(preds[,i],ROCR.simple$labels),"tpr","fpr"), 
                                           add=(i!=1),col=colors[i],lwd=2)
}

Answer 2

The plot function for ROCR objects does not seem to offer this option. So, you'll have to pick apart the object and do it manually.

For instance, using ggplot2 ,

library(ggplot2)
df <- data.frame(Curve=as.factor(rep(c(1,2), each=length(perf.mat@x.values[[1]]))), 
                 FalsePositive=c(perf.mat@x.values[[1]],perf.mat@x.values[[2]]),
                 TruePositive=c(perf.mat@y.values[[1]],perf.mat@y.values[[2]]))
plt <- ggplot(df, aes(x=FalsePositive, y=TruePositive, color=Curve)) + geom_line()
print(plt)

Answer 3

You can use just plot with add=TRUE

pred <- prediction( predicted1, response )
pred2 <- prediction(predicted2, response)
perf <- performance( pred, "tpr", "fpr" )
perf2 <- performance(pred2, "tpr", "fpr")
plot( perf, colorize = FALSE,  type="l",col="blue")
abline(a=0,b=1)
plot(perf2,colorize = FALSE, add = TRUE,  type="l", lty=3,col="black")