$ 死亡:Classes ‘tbl_df’, ‘tbl’ and 'data.frame':
..$ ID : chr [1:3]
..$ age : chr [1:3] "53" "70" "61"
..$ Dose : chr [1:3] "50" "150" "75"
如上面已经读取的数据类型,age,dose都是chr类型的,如何将其改为num(改完后保存到原来的dataframe中)?试过as.numeric(),报错,Error: (list) object cannot be coerced to type 'double'