R中的小鼠问题：不能将类“mids”强制转换为data.frame

I have a dataset with about 11,500 rows and 15 factors. I only need to impute values for 3 of the factors, with only 2 of the factors having any significant number of missing values. I have been trying to use mice to create imputed datasets, and I am using the following code:I have a dataset with about 11,500 rows and 15