在R中返回对象或多个变量（非数字）

Question

I am training multiple SVMs in my R application, and I would like my function to return a holder object to which I can easily access each one of them later in a function.

The SVM is created as this:

svm.model <- svm(x=trainset,y=trainlabels)
svm.pred <- predict(svm.model,testset)

res <- table(pred = svm.pred, true = testlabels)  

I want to be able to return the table called "res", or both svm.model and svm.pred. Any will do.

In a Object Oriented language I would use something like Javas ArrayList to do this, but a regular list(which was suggested in many posts) didn't do its job. I was not able to put any of these values, and if I made it, they got "unwrapped" and lost its structure.

Update Good point in the comment section about how exactly I tried to do this with a list. I did the following:

result<-list()

for i in...
   result[i]<-svm.model
   result[i+1] <-svm.pred

I have tried the same as above, but with "res"(a table).

Another approach I tried was to create a new list with the previous list each time: result<-list(result,svm.model,svm.pred)

It gives me only a length 3 size list(I see why) and the two last values are "lists" instead of what they are in fact, hence it doesn't allow me to call "table(pred = svm.pred, true = testlabels) " as it returns an error:

"Error in sort.list(y) : 'x' must be atomic for 'sort.list' Have you called 'sort' on a list?"

Answer 1

If you have a loop and you want to store all three

result<-list()
for (i in 1:n) {
    ...
    svm.model <- svm(x=trainset,y=trainlabels)
    svm.pred <- predict(svm.model,testset)

    res <- table(pred = svm.pred, true = testlabels)  
    result[[i]] <- list(res=res, svm.model=svm.model, svm.pred=svm.pred)
}

Note is is important to use [[ ]] when putting items into a list and getting them out. I also used a named list here to make it easier to get specific objects out. Then if you wanted to re-make the table from the 3rd loop, you could do

table(pred = result[[3]]$svm.pred, true=testlabels)

Answer 2

Thank you for the answer! I managed to overcome it also by doing the following:

result[folders[i]]<-list(res)

Where folders is a vector of names. :-)