我正在使用tidymodels方法创建一个随机森林模型。在recipe函数中，我得到了这个错误/警告，我根本无法解释，但它必须与创建的汇总变量相关。错误是

There are new levels in a factor: NA

所以，现在我的食谱参数看起来像这样：

era.af.Al_rec <- recipes::recipe(logRR ~., data = era.af.Al_predict) %>%
  step_mutate_at(logRR, SubPrName, PrName, Product, AEZ16simple, fn = factor) %>%
  update_role(ID, new_role = "ID") %>%
  update_role(RR_group, new_role = "ID") %>%
  step_other(SubPrName, PrName, Product, AEZ16simple, threshold = 0.01) %>%
  step_other(Site.ID, threshold = 0.001) %>%
  step_dummy(all_nominal(), -all_outcomes()) %>%
  step_downsample(logRR)

era.af.Al_prep <- prep(era.af.Al_rec)

juiced <- juice(era.af.Al_prep)

错误在_prep调用中弹出。