R中行的有序分组

Question

我想创建一个新列，以按顺序标记行组。原始数据：

> dt = data.table(index=(1:10), group = c("apple","apple","orange","orange","orange","orange","apple","apple","orange","apple"))
> dt
    index  group
 1:     1  apple
 2:     2  apple
 3:     3 orange
 4:     4 orange
 5:     5 orange
 6:     6 orange
 7:     7  apple
 8:     8  apple
 9:     9 orange
10:    10  apple

所需的输出：

    index  group id
 1:     1  apple  1
 2:     2  apple  1
 3:     3 orange  1
 4:     4 orange  1
 5:     5 orange  1
 6:     6 orange  1
 7:     7  apple  2
 8:     8  apple  2
 9:     9 orange  2
10:    10  apple  3

dplyr 尝试：

dt %>% group_by(group) %>% mutate( id= row_number())
# A tibble: 10 x 3
# Groups:   group [2]
   index group     id
   <int> <chr>  <int>
 1     1 apple      1
 2     2 apple      2
 3     3 orange     1
 4     4 orange     2
 5     5 orange     3
 6     6 orange     4
 7     7 apple      3
 8     8 apple      4
 9     9 orange     5
10    10 apple      5

我该如何编辑以使第一组苹果为1，然后第一组橙子为1，然后第二组苹果为2，依此类推（请参见上面的期望输出）。也开放data.table解决方案。

Answer 1

library(data.table)
dt[, id := cumsum(c(TRUE, diff(index) > 1)), by="group"]
dt
#     index  group id
#  1:     1  apple  1
#  2:     2  apple  1
#  3:     3 orange  1
#  4:     4 orange  1
#  5:     5 orange  1
#  6:     6 orange  1
#  7:     7  apple  2
#  8:     8  apple  2
#  9:     9 orange  2
# 10:    10  apple  3

从原始开始dt：

library(dplyr)
dt %>%
  group_by(group) %>%
  mutate(id = cumsum(c(TRUE, diff(index) > 1))) %>%
  ungroup()
# # A tibble: 10 x 3
#    index group     id
#    <int> <chr>  <int>
#  1     1 apple      1
#  2     2 apple      1
#  3     3 orange     1
#  4     4 orange     1
#  5     5 orange     1
#  6     6 orange     1
#  7     7 apple      2
#  8     8 apple      2
#  9     9 orange     2
# 10    10 apple      3

基数R，可能有点笨拙：

out <- do.call(rbind, by(dt, dt$group,
                         function(x) transform(x, id = cumsum(c(TRUE, diff(index) > 1)))))
out[order(out$index),]
#          index  group id
# apple.1      1  apple  1
# apple.2      2  apple  1
# orange.3     3 orange  1
# orange.4     4 orange  1
# orange.5     5 orange  1
# orange.6     6 orange  1
# apple.7      7  apple  2
# apple.8      8  apple  2
# orange.9     9 orange  2
# apple.10    10  apple  3

使用可以轻松删除名称rownames(out) <- NULL。该order部分不是必需的，但是我想以与其他解决方案相同的顺序来呈现它，并且do.call/ by不会保留原始顺序。