r - 如何使用正则表达式和 R 提取匹配项上方的行？

Question

我想使用 R 匹配一些特定的字符串并只保留匹配项上方的行，这是一些示例数据。有一个包含数百个类似案例的文件:

first_case<- data.frame(line = 

             c("#John Wayne: Su, 11.01.2013 08:24:42#
                He is present / I guess, Does great job
                --------------------------------------------------
                #Michal Thorn: Fr, 12.09.2015 17:23:01#
                Works quite frequently with people
                --------------------------------------------------
                #Sandra Nunes: Mo, 20.05.2011 09:00:29#
                She has some new clients"))



second_case<- data.frame(line = 

                c("#Boris Jonson: Mo, 30.09.2017 09:20:42#
                He is present
                --------------------------------------------------
                #Jacky Fine: Th, 02.02.2013 18:23:01#
                Does great job
                --------------------------------------------------
                #Michael Bissping: Mo, 25.03.2012 10:00:29#
                Hard to count on"))



third_case<- data.frame(line = 

              c("#Isabelle Warren: Sa, 02.12.2013 02:24:42#
                 Not around / anymore
               --------------------------------------------------
                 #Tobias Maker: Mo, 02.03.2013 10:23:01#
                 Works quite frequently with people
               --------------------------------------------------
                 #Toe Michael : Mo, 20.05.2011 09:00:29#
                 She has some new clients & Does great job"))

all_cases <- rbind(first_case,second_case,third_case)

在这里，我尝试过滤上面 1 行的那些行:
Does great job
通过查看是否 Does great job以新行结束并取上面的第一行:

dplyr::filter(all_cases, grepl("((.*\n){1})Does great job",line))

预期成绩:

first_case<- data.frame(line = 
                      c("#John Wayne: Su, 11.01.2013 08:24:42#"))
second_case<- data.frame(line = 
                       c("#Jacky Fine: Th, 02.02.2013 18:23:01#"))
third_case<- data.frame(line = 
                      c("#Toe Michael : Mo, 20.05.2011 09:00:29#"))

expected_result <- rbind(first_case,second_case,third_case)

1   #John Wayne: Su, 11.01.2013 08:24:42#
2   #Jacky Fine: Th, 02.02.2013 18:23:01#
3   #Toe Michael : Mo, 20.05.2011 09:00:29#

不幸的是，这将返回零行。欣赏任何见解!

Answer 1

这是使用 strsplit 的一种基本 R 方法.我们可以形成一个行的列表/向量，然后直接使用grep找到匹配 Does great job 的行的索引.然后，只需返回紧随其后的行。

line <- "#Boris Jonson: Mo, 30.09.2017 09:20:42#
         He is present
         --------------------------------------------------
         #Jacky Fine: Th, 02.02.2013 18:23:01#
         Does great job
         --------------------------------------------------
         #Michael Bissping: Mo, 25.03.2012 10:00:29#
         Hard to count on"

terms <- unlist(strsplit(line, "\n"))
terms[grep("Does great job", terms) - 1]

[1] "                #Jacky Fine: Th, 02.02.2013 18:23:01#"

Demo

我的回答没有涵盖许多边缘情况，第一个是匹配逻辑。如果搜索词匹配多次或根本不匹配，会发生什么情况？另外， grep 中使用的模式应该如何具体？是？