[R] Can this code be written more efficiently?

[Guelman, Leo]

Dear users,

I'm working on binary classification problem using Support Vector
Machines (SVM). My objective is to train a series of SVM models on a
grid of hyperparameters and then select those that maximize the AUC
based on an independent validation sample. 

My attempted code is shown below. It runs well on "small" data sets but
when I use it on a slightly larger sample (e.g., my train data is
composed of about 8,000 observations on each class and 21 inputs), it
takes "forever" to run (more than 1 day already and still running). I'm
wondering if there's any way I can optimize this code. Thanks in advance
for any help.

I'm using 64-bit R 2.11.1 on Win 7. 

####Start Code####

library(e1071)
library(ROCR)

### Create grid of hyperparameters

Gseq <- seq(-15,3,2); G <- rep(2, length(Gseq)); G <- G^Gseq
Cseq <- seq(-5,13,2); C <- rep(2, length(Cseq)); C <- C^Cseq
mygrid <- expand.grid(C=C, G=G)

### Train models

svm.models <-  lapply(1:nrow(mygrid), function(i) {
                svm(churn.form, data = mytraindata,
                method = "C-classification", kernel = "radial",
                cost = mygrid[i,1], gamma = mygrid[i,2],
probability=TRUE)
                })

### Predict on test set 

pred.step3 <- numeric(length(svm.models))

for (i in 1:length(svm.models)) {

pred.step1 <- predict(svm.models[[i]], myvaliddata, decision.values = F,

              probability=T)

pred.step2 <-
prediction(predictions=attr(pred.step1,"probabilities")[,1],
labels=myvaliddata$churn)

pred.step3[i] <- performance(pred.step2, "auc")@y.values[[1]]

}

pred.step3

####End Code####


Thanks,
Leo.

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