虽然参数匹配文档，但Svyby返回错误

Question

我使用调查包定义了一个调查对象（一切正常），并按如下方式添加了两列：

anes_svy <- update( #the update fn adds columns to a survey object
  anes_svy, #object to add variables to
  one = 1,
  undoc_kids =
            factor( V161195x , levels = 1:6 , labels =
                c( 'should sent back - favor a great deal' ,
                   'should sent back - favor a moderate amount' ,
                   'should sent back - favor a little' ,
                   'should allow to stay - favor a little' ,
                   'should allow to stay - favor a moderate amount' ,
                   'should allow to stay - favor a great deal' )
            )
)

现在我跑

svyby( formula = ~one , by = ~undoc_kids , design = anes_svy , FUN = unwtd.count )

我收到错误

Error in sum(sapply(covmats, ncol)) : invalid 'type' (list) of argument

文档要求'公式'的向量，'by'的因子列表，'design'的svydesign对象，以及FUN的函数（unwtd.count是内置的）。我做错了什么？