R tidyr使用技巧：如何让fill函数填充到最后一个匹配模式行后停止

实现方法 #

核心逻辑是先定位到((s: End))对应的行号，仅对该行及之前的部分执行向下填充，后续行不填充直接保留NA即可。

完整代码如下：

library(dplyr)
library(tidyr)

# 原始数据
df <- structure(list(line = c("001", "002", "003", "004", "005", "006", 
                              "007", "008", "009", "010", "011", "012", "013", "014"), 
                     utterance = c("((m: both hands", 
                                   "((m: both hands", 
                                   "((i: DH=1, SZ=0", "((i: DH=1, SZ=0", 
                                   "((s: Preface))", "((m: both hands", 
                                   "((m: both hands clasped", 
                                   "((m: both hands clasped", 
                                   "((s: Background))", "((m: enumerating", 
                                   "((m: enumerating", 
                                   "((s: End))", "((i: DH=1, SZ=0", "((m: relax gesture))"
                              )), row.names = c(NA, 14L), class = "data.frame")

# 定位((s: End))所在行号
end_row <- which(df$utterance == "((s: End))")

df %>%
  # 生成初始story列，匹配((s的行保留原值，其余为NA
  mutate(story = ifelse(grepl("\\(\\(s", utterance), utterance, NA)) %>%
  # 取End行及之前的部分做向下填充
  slice(1:end_row) %>%
  fill(story, .direction = "down") %>%
  # 拼接End行之后的内容，story列默认补NA
  bind_rows(df %>% slice(-(1:end_row)))

运行后输出结果和预期完全一致：

line               utterance             story
1   001         ((m: both hands              <NA>
2   002         ((m: both hands              <NA>
3   003         ((i: DH=1, SZ=0              <NA>
4   004         ((i: DH=1, SZ=0              <NA>
5   005          ((s: Preface))    ((s: Preface))
6   006         ((m: both hands    ((s: Preface))
7   007 ((m: both hands clasped    ((s: Preface))
8   008 ((m: both hands clasped    ((s: Preface))
9   009       ((s: Background)) ((s: Background))
10  010        ((m: enumerating ((s: Background))
11  011        ((m: enumerating ((s: Background))
12  012              ((s: End))        ((s: End))
13  013         ((i: DH=1, SZ=0              <NA>
14  014    ((m: relax gesture))              <NA>

内容的提问来源于stack exchange，提问作者Chris Ruehlemann