我有以下数据框，我只需要过滤那些每组（id）同时具有“摄入”和“排出”的行。结果应该是这样的：
> df <- tibble(id = c(1, 1, 2, 3, 3, 4, 4, 5, 6, 7, 7),
+ type = c("intake", "discharge", "intake", "intake", "discharge",
+ "intake", "discharge", "intake", "intake", "intake", "discharge"))
> df
id type
<dbl> <chr>
1 1 intake
2 1 discharge
3 2 intake
4 3 intake
5 3 discharge
6 4 intake
7 4 discharge
8 5 intake
9 6 intake
10 7 intake
11 7 discharge
对此：
id type
<dbl> <chr>
1 1 intake
2 …