Question

我有一个数据框，列出了参加活动的学生总数（Stu）和每组学生人数（ID）：

     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

我想知道参与活动（Sub＆gt; 0）或不参与活动的大小范围（> 400，＆gt; 200，＆gt; 100，＆gt; 0）的群组数量（Sub is.na）

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

但我明白了：

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

如何使总结中的长度函数像countif一样？

Answer 1

summarise需要一个值，因此sum代替length完成工作：

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

Answer 2

遵循@ eipi10提供的相同想法，但切入count()而不是group_by() %>% tally()，并显示tidyr::spread可以模仿reshape2::dcast：

output %>%
  count(Sub = ifelse(is.na(Sub), 'No Entries', 'Entires'),
        Stu = cut(Stu, c(0, 100, 200, 400, +Inf), labels = c(0, 100, 200, 400))) %>%
  tidyr::spread(Sub, n, fill = 0)

Answer 3

另一种选择是按Stu和Sub进行分组，但要做到这一点，我们需要先重新编码Sub和Stu的值以匹配输出分组我们想要。我们还使用cut而不是嵌套ifelse来设置Stu中的值分隔符：

library(reshape2)

output %>% 
  group_by(Sub=ifelse(is.na(Sub), "No Entries", "Entries"),
           Stu=cut(Stu, c(0,100,200,400,Inf), labels=c(0,100,200,400))) %>%
  tally %>%
  dcast(Stu ~ Sub, fill=0)

     Stu Entries No Entries
1      0       0          2
2    100       0          3
3    200       1          0

在dplyr中等同于COUNTIF

3 个答案: