for(i in 1:10){
testIndexes <- which(folds==i,arr.ind=TRUE)
testData <- yourData[testIndexes, ]
trainData <- yourData[-testIndexes, ]

if(i==1){
   set.seed=1234
   Subtest = data.frame(i,sample(nrow(trainData) , size = round(0.3*(nrow(trainData))),replace=F),trainData)
}else{
  Subtest = rbind(data.frame(sample(nrow(trainData) , size = round(0.3*(nrow(trainData)))),
                        i,trainData))
}
}

Error in data.frame(i, sample(nrow(trainData), size = round(0.3 * (nrow(trainData))),  :
  arguments imply differing number of rows: 1, 81, 270