根据 R 中的行号重组数据

Question

我在按需要重组数据时遇到问题。我的 df 看起来像这样:

id <- (1:20)
author <- c("A","A","A","A","A","B","B","B","A","A","A","B","B","B","B"
            ,"B","B","B","A","A")
df <- data.frame(id, author)

> print(df)

   id author
1   1      A
2   2      A
3   3      A
4   4      A
5   5      A
6   6      B
7   7      B
8   8      B
9   9      A
10 10      A
11 11      A
12 12      B
13 13      B
14 14      B
15 15      B
16 16      B
17 17      B
18 18      B
19 19      A
20 20      A

我正在尝试获取一个数据结构，其中列是作者，rwos 指示每个 A 或 B 值序列的第一个和最后一个 id 值。所以在这种情况下，作者 A 的第一行是 id = 1，该系列的最后一行是 id 5，依此类推。像这样:

A <- c(1, 5, 9, 11, 19,20)
B <- c(6, 8, 12, 18, NA, NA)
df.desired <- data.frame(A, B)
print(df.desired)
   A  B
1  1  6
2  5  8
3  9 12
4 11 18
5 19 NA
6 20 NA 

有什么想法吗？非常感谢!

Answer 1

我们可以使用 data.table rleid 创建组，选择每个组中的第一行和最后一行并获取宽格式的数据。

library(dplyr)

df %>%
  group_by(grp = data.table::rleid(author)) %>%
  slice(1L, n()) %>%
  group_by(author) %>%
  mutate(grp = row_number()) %>%
  tidyr::pivot_wider(names_from = author, values_from = id) %>%
  select(-grp)

# A tibble: 6 x 2
#      A     B
#  <int> <int>
#1     1     6
#2     5     8
#3     9    12
#4    11    18
#5    19    NA
#6    20    NA

---

对于评论中的更新请求，我们可以这样做:

df %>%
  group_by(grp = data.table::rleid(author)) %>%
  slice(1L, n()) %>%
  mutate(author = row_number()) %>%
  tidyr::pivot_wider(names_from = row, values_from = id) %>%
  ungroup %>%
  select(-grp)

# A tibble: 5 x 2
#    `1`   `2`
#  <int> <int>
#1     1     5
#2     6     8
#3     9    11
#4    12    18
#5    19    20