r - COUNTIF 相当于 dplyr 总结

Question

我有一个数据框，列出了参加事件的学生总数 (Stu) 和每组学生人数 (ID) (Sub):

     ID   Stu   Sub
  (int) (int) (int)
1   101    80    NA
2   102   130    NA
3   103    10    NA
4   104   210    20
5   105   180    NA
6   106   150    NA

我想知道参与某项事件 (Sub > 0) 或不参与某项事件 (Sub is.na) 的大小范围 (>400、>200、>100、>0) 中的群体数量

output <- structure(list(ID = c(101L, 102L, 103L, 104L, 105L, 106L), 
                       Stu = c(80L, 130L, 10L, 210L, 180L, 150L), 
                       Sub = c(NA,NA, NA, 20L, NA, NA)), 
                  .Names = c("ID", "Stu", "Sub"), 
                  class = c("tbl_df", "data.frame"), 
                  row.names = c(NA, -6L))

temp <- output %>% 
mutate(Stu = ifelse(Stu >= 400, 400,
         ifelse(Stu >= 200, 200,
             ifelse(Stu >= 100, 100, 0
                 )))) %>%
group_by(Stu) %>%
summarise(entries = length(!is.na(Sub)),
          noentries = length(is.na(Sub)))

结果应该是:

    Stu entries noentries
  (dbl)   (int)     (int)
1     0       0         2
2   100       0         3
3   200       1         0

但我得到:

    Stu entries noentries
  (dbl)   (int)     (int)
1     0       2         2
2   100       3         3
3   200       1         1

如何使summary中的长度函数像countif一样？

Answer 1

summarise 需要一个值，因此使用 sum 而不是 length 来完成这项工作:

output %>% 
  mutate(Stu = ifelse(Stu >= 400, 400,
                      ifelse(Stu >= 200, 200,
                             ifelse(Stu >= 100, 100, 0
                             )))) %>%
  group_by(Stu) %>% 
  summarise(entries = sum(!is.na(Sub)),
            noentries = sum(is.na(Sub)))

Source: local data frame [3 x 3]

Stu entries noentries
(dbl)   (int)     (int)
1     0       0         2
2   100       0         3
3   200       1         0