[R] ROCR package question

[Waverley]

I use ROCR to plot multiple runs' performance.  Using the sample code
as example:

# plot ROC curves for several cross-validation runs (dotted
# in grey), overlaid by the vertical average curve and boxplots
# showing the vertical spread around the average.
data(ROCR.xval)
pred <- prediction(ROCR.xval$predictions, ROCR.xval$labels)
perf <- performance(pred,"tpr","fpr")
plot(perf,col="grey82",lty=3)
plot(perf,lwd=3,avg="vertical",spread.estimate="boxplot",add=TRUE)

I can follow the code and plot without any problem.  However, I don't
know how to extract the averaged ROC area under curve value.

Can someone help?

Thanks.

-- 
Waverley @ Palo Alto