knnoutput <- knnImputation(mydata)
Error in knnImputation(mydata) :
  Not sufficient complete cases for computing neighbors.
In addition: Warning message:
In knnImputation(mydata) : NAs introduced by coercion
这个不行，显示错误

miceMod <- mice(mydata, m = 5, method = "rf")

iter imp variable
  1   1  BError in ranger::ranger(x = xobs, y = yobs, num.trees = ntree) :
  Error: No covariates found.
这个也是不可以的，但是“pmm”，“norm”都可以，是为什么呢？