Hello,

I'm using ROCR to plot ROC Curves and I want to automate the saving of plots
into PNG files using a custom function.

My data frames are named like test1, test2, test3. Each data frame has three
variables: method1, method2, goldstandard.

Right now, for each plot I have to run:

png('test1_method1.png')
plot(performance(prediction(test1$method1, test1$goldstandard), "tpr",
"fpr"))
dev.off()

Here is the function I tried to create but I failed:

roc <- function(arg1, arg2){
  png(paste(arg1, arg2, "png", sep="_"))
  plot(performance(prediction(arg1$arg2, arg1$goldstandard), "tpr", "fpr"))
  dev.off()
}

I wanted to pass the test name as arg1, and the method name as arg2. Here
are my problems:

1) arg1$arg2 causes an error message. How can I use a function argument to
address a variable in a dataframe?

2) paste(arg1, arg2, "png", sep=".") doesn't output something like
'test1.method1.png'. How should I deal with that?

Thanks in advance.

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