传入for循环函数中的变量列表

Question

我在矢量中有一个变量名列表，我希望将其传递给函数，从输出中获取这些数据帧，并在循环的下一次迭代中用作函数的参数。

standardized_funct= function(train,test, my_variable) {

  #handle missing values
   train$my_variable =  ifelse(is.na(train$my_variable)==TRUE, 'MISSING',my_variable)

   my_variable=eval(substitute(my_variable))

  # handle missing values and set factors equivalent
  test$my_variable = ifelse(is.na(test$my_variable)==TRUE, 'MISSING',my_variable)
    test$my_variable = factor(test$my_variable, levels = base::unique(train$my_variable))


  train$my_variable = 
     factor(train$my_variable)

  output_factors = list(TRAIN = train, TEST = test)
  return(output_factors)
}   


   # setup dummy data
   rm(mtcars)
    mtcars2 = rbind(mtcars,mtcars)
   list_of_var = c("hp","mpg",'cyl')

  for (each_variable in list_of_var){

outputdf =  standardized_funct(train = mtcars, test = mtcars2, my_variable = each_variable

mtcars = outputdf$TRAIN
mtcars2 = outputdf$TEST
  # should loop through each variable and run the function...that transforms the values to factor
}