使用 ROCit 绘制多条 ROC 曲线

Question

I wanted to use ROCit for creating ROC curves. But I can not figure out, how to plot two ROC curves in the same plot.

For example:

data("Diabetes")
library(ROCit)
plot(rocit(score = Diabetes$chol, class = Diabetes$dtest, negref = "-"))
par(new=TRUE)
plot(rocit(score = Diabetes$bmi, class = Diabetes$dtest, negref = "-"))

Using the par command in between, I can get it to work, but I would had to set the colors all manually and also the legend does not correctly reflect the data.

Is it somehow possible to use ROCit to compare different models in the same plot?

Answer 1

You plot the first ROCit object, then add lines for subsequent ones.

Note that the subsequent ones are specified as $TPR ~ $FPR (for some reason).

data(Diabetes)
library(ROCit)

# ROCit objects
roc_emp1 <- rocit(score = Diabetes$chol, class = Diabetes$dtest, negref = "-") 
roc_emp2 <- rocit(score = Diabetes$bmi, class = Diabetes$dtest, negref = "-") 

# plot the first, then the second, then add the legend
plot(roc_emp1, col = c(1,"gray50"), 
     legend = FALSE, YIndex = FALSE)
lines(roc_emp2$TPR ~ roc_emp2$FPR, 
      col = 2, lwd = 2)
legend("bottomright", col = c(1,2),
       c("Empirical ROC 1", "Empirical ROC 2"), lwd = 2)