R:如何连接分成多行的字符串？

Question

我有一个如下所示的数据框:

df1 <- data.frame(Question=c("This is the start", "of a question", "This is a second", "question"), 
  Answer = c("Yes", "", "No", ""))

           Question Answer
1 This is the start    Yes
2     of a question       
3  This is a second     No
4          question       

这是虚拟数据，但真实数据是通过制表器从 PDF 中提取的。只要源文档中的 Question 出现换行符，该问题就会分成多行。如何根据 Answer 为空的条件串联回去？

想要的结果很简单:

                     Question     Answer
1 This is the start of a question    Yes
2       This is a second question     No

逻辑很简单，如果 Answer[x] 为空，则连接 Question[x] 和 Question[x-1] 并删除行x。

Answer 1

这无疑可以改进，但如果您乐意使用 tidyverse，也许这样的方法可以工作？

library(dplyr)
library(tidyr)
library(stringr)

df1 %>% 
  mutate(id = if_else(Answer != "", row_number(), NA_integer_)) %>%
  fill(id) %>% group_by(id) %>%
  summarise(Question = str_c(Question, collapse = " "), Answer = first(Answer))

#> # A tibble: 2 x 3
#>      id                        Question Answer
#>   <int>                           <chr> <fctr>
#> 1     1 This is the start of a question    Yes
#> 2     3       This is a second question     No