Using the R package caret, how can I generate a ROC curve based on the cross-validation results of the train() function?
Say, I do the following:
data(Sonar)
ctrl <- trainControl(method="cv",
summaryFunction=twoClassSummary,
classProbs=T)
rfFit <- train(Class ~ ., data=Sonar,
method="rf", preProc=c("center", "scale"),
trControl=ctrl)
The training function goes over a range of mtry parameter and calculates the ROC AUC. I would like to see the associated ROC curve -- how do I do that?
Note: if the method used for sampling is LOOCV, then rfFit
will contain a non-null data frame in the rfFit$pred
slot, which seems to be exactly what I need. However, I need that for the "cv" method (k-fold validation) rather than LOO.
Also: no, roc
function that used to be included in former versions of caret is not an answer -- this is a low level function, you can't use it if you don't have the prediction probabilities for each cross-validated sample.
There is just the savePredictions = TRUE
argument missing from ctrl
(this also works for other resampling methods):
library(caret)
library(mlbench)
data(Sonar)
ctrl <- trainControl(method="cv",
summaryFunction=twoClassSummary,
classProbs=T,
savePredictions = T)
rfFit <- train(Class ~ ., data=Sonar,
method="rf", preProc=c("center", "scale"),
trControl=ctrl)
library(pROC)
# Select a parameter setting
selectedIndices <- rfFit$pred$mtry == 2
# Plot:
plot.roc(rfFit$pred$obs[selectedIndices],
rfFit$pred$M[selectedIndices])
Maybe I am missing something, but a small concern is that train
always estimates slightly different AUC values than plot.roc
and pROC::auc
(absolute difference < 0.005), although twoClassSummary
uses pROC::auc
to estimate the AUC. Edit: I assume this occurs because the ROC from train
is the average of the AUC using the separate CV-Sets and here we are calculating the AUC over all resamples simultaneously to obtain the overall AUC.
Update Since this is getting a bit of attention, here's a solution using plotROC::geom_roc()
for ggplot2
:
library(ggplot2)
library(plotROC)
ggplot(rfFit$pred[selectedIndices, ],
aes(m = M, d = factor(obs, levels = c("R", "M")))) +
geom_roc(hjust = -0.4, vjust = 1.5) + coord_equal()
Here, I'm modifying the plot of @thei1e which others may find helpful.
Train model and make predictions
library(caret)
library(ggplot2)
library(mlbench)
library(plotROC)
data(Sonar)
ctrl <- trainControl(method="cv", summaryFunction=twoClassSummary, classProbs=T,
savePredictions = T)
rfFit <- train(Class ~ ., data=Sonar, method="rf", preProc=c("center", "scale"),
trControl=ctrl)
# Select a parameter setting
selectedIndices <- rfFit$pred$mtry == 2
Updated ROC curve plot
g <- ggplot(rfFit$pred[selectedIndices, ], aes(m=M, d=factor(obs, levels = c("R", "M")))) +
geom_roc(n.cuts=0) +
coord_equal() +
style_roc()
g + annotate("text", x=0.75, y=0.25, label=paste("AUC =", round((calc_auc(g))$AUC, 4)))