ggolot2 画ROC曲线

####获取画图数据（data.frame格式)#####
library(ggplot2)
library(ROCR) ##用于计算ROC
data(ROCR.simple) ###画图数据集
pred <- prediction(ROCR.simple$predictions, ROCR.simple$labels)  
perf <- performance(pred,"tpr","fpr") 
x <- unlist(perf@x.values)  ##提取x值
y <- unlist(perf@y.values)
plotdata <- data.frame(x,y) 
names(plotdata) <- c("x", "y")
#####画图###############
##先确定映射图层geom_path,labs层修改标题，scale_colour_gradient层修改图例（为何是这个看2.0），theme层精细修改标题。##  
g <- ggplot(plotdata) + 
  geom_path(aes(x = x, y = y, colour = x), size=1) + 
  labs(x = "False positive rate", y = "Ture positive rate", title ="ROC曲线") +
  scale_colour_gradient(name = 'False positive rate', low = 'blue', high = 'red') +
  theme(plot.title = element_text(face = 'bold',size=15))
g