Question

我有一个数据框（df）：

a <- c("up","up","up","up","down","down","down","down")
b <- c("l","r","l","r","l","l","r","r")


df <- data.frame(a,b)

我想添加第三列（c），其中包含条目顺序，按a和b列分组，如下所示：

   a   b c
1   up l 1
2   up r 1
3   up l 2
4   up r 2
5 down l 1
6 down l 2
7 down r 1
8 down r 2

我尝试过使用dplyr的解决方案但没有工作：

order <- df %>%
   group_by(a) %>%
   group_by(b) %>%
   mutate(c = row_number()) # This counts the order based on `b`, ignoring `a`

order <- df %>%
       group_by(a) %>%
       group_by(b) %>%
       mutate(c = seq_len(n())) # This counts the order based on `b`, ignoring `a`

如果可能的话，我更愿意继续使用dplyr和管道，但欢迎提出其他建议

Answer 1

您需要在同一a声明中合并b和group_by。

order <- df %>%
  group_by(a, b) %>%
  mutate(c = row_number()) 

order

# Source: local data frame [8 x 3]
# Groups: a, b [4]
# 
#       a      b     c
#   <fctr> <fctr> <int>
# 1     up      l     1
# 2     up      r     1
# 3     up      l     2
# 4     up      r     2
# 5   down      l     1
# 6   down      l     2
# 7   down      r     1
# 8   down      r     2

两个因子group_by然后添加行号R dplyr

1 个答案: