在运行随机森林模型的脚本时，遇到报错。
data.all <- read.csv("myotu.csv", head = T, row.names = 1)
set.seed(9)
folds <- createFolds(y=data.all$Group,k=10)
for(i in 1:10){
  fold_test <- data.all[folds,]
  fold_train <- data.all[-folds,]  
  fold_pre <-randomForest(data.all[,31] ~ .,data= fold_train, mtry=5.5,ntree=500, proximity=TRUE,importance=TRUE)}
Error in model.frame.default(formula = data.all[, 31] ~ ., data = fold_train,  : 变数的长度不一样('OTU16')
试过修改文件格式为txt没有用，求帮忙指点一二，谢谢！

附上‘OTU16’此列数据