R 正则表达式提取文本不立即遵循模式

Question

我有一个数据框架，其中一列包含半结构化文本。我在寻找某些信息，但它们有一种模式，我不知道如何利用。

head(events5)
     flight_history_id         date_time_recorded              event
862          280604281 2012-11-13 17:55:58.673-08 Arrival Estimation
5514         280316415 2012-11-12 17:25:08.814-08    Time Adjustment
5527         280315758 2012-11-12 16:10:06.968-08    Time Adjustment
5539         280316495 2012-11-12 15:38:10.099-08    Time Adjustment
5545         280303866 2012-11-13 06:51:45.831-08    Time Adjustment
5558         280303866 2012-11-12 05:50:23.547-08    Time Adjustment
                                                                               data_updated
862                                                     EGA- Based on Distance and Airspeed
5514                        EGD- New=11/13/12 20:20, DGATE- New=A1, EGA- New=11/13/12 21:00
5527         EGD- New=11/13/12 19:05, DGATE- New=A7, EGA- New=11/13/12 20:50, AGATE- New=C5
5539                        EGD- New=11/13/12 06:35, DGATE- New=A1, EGA- New=11/13/12 07:15
5545 AGD- Old=11/13/12 07:40 New=11/13/12 07:38, EGA- Old=11/13/12 10:25 New=11/13/12 10:18
5558         EGD- New=11/13/12 07:45, DGATE- New=11, EGA- New=11/13/12 10:25, AGATE- New=A1

这是 DPUT：

structure(list(flight_history_id = c(280604281L, 280316415L, 
280315758L, 280316495L, 280303866L, 280303866L, 280271465L, 280271465L, 
280271465L, 280271465L), date_time_recorded = structure(c(10L, 
4L, 3L, 2L, 7L, 1L, 9L, 8L, 6L, 5L), .Label = c("2012-11-12 05:50:23.547-08", 
"2012-11-12 15:38:10.099-08", "2012-11-12 16:10:06.968-08", "2012-11-12 17:25:08.814-08", 
"2012-11-12 17:58:14.268-08", "2012-11-13 05:16:41.01-08", "2012-11-13 06:51:45.831-08", 
"2012-11-13 07:38:19.593-08", "2012-11-13 07:54:22.588-08", "2012-11-13 17:55:58.673-08"
), class = "factor"), event = structure(c(1L, 2L, 2L, 2L, 2L, 
2L, 2L, 2L, 2L, 2L), .Label = c("Arrival Estimation", "Time Adjustment"
), class = "factor"), data_updated = structure(c(3L, 8L, 7L, 
4L, 2L, 5L, 1L, 10L, 9L, 6L), .Label = c("AGD- New=11/13/12 10:22, EGA- Old=11/13/12 11:20 New=11/13/12 11:09", 
"AGD- Old=11/13/12 07:40 New=11/13/12 07:38, EGA- Old=11/13/12 10:25 New=11/13/12 10:18", 
"EGA- Based on Distance and Airspeed", "EGD- New=11/13/12 06:35, DGATE- New=A1, EGA- New=11/13/12 07:15", 
"EGD- New=11/13/12 07:45, DGATE- New=11, EGA- New=11/13/12 10:25, AGATE- New=A1", 
"EGD- New=11/13/12 08:55, EGA- New=11/13/12 09:45, AGATE- New=A1", 
"EGD- New=11/13/12 19:05, DGATE- New=A7, EGA- New=11/13/12 20:50, AGATE- New=C5", 
"EGD- New=11/13/12 20:20, DGATE- New=A1, EGA- New=11/13/12 21:00", 
"EGD- Old=11/13/12 08:55 New=11/13/12 10:05, EGA- Old=11/13/12 09:45 New=11/13/12 10:55", 
"EGD- Old=11/13/12 10:05 New=11/13/12 10:30, EGA- Old=11/13/12 10:55 New=11/13/12 11:20"
), class = "factor")), .Names = c("flight_history_id", "date_time_recorded", 
"event", "data_updated"), row.names = c(862L, 5514L, 5527L, 5539L, 
5545L, 5558L, 5564L, 5566L, 5570L, 5572L), class = "data.frame")

我正在尝试从“data_updated”列中提取以“EGA”开头的部分的字段“New=”部分。问题是有时两者之间有一个“Old=”字段。我查看了使用 stringr：：str_split 并将列转换为列表，但仍然有同样的问题。我认为这是一个正则表达式/gsub 问题，但不确切知道如何实现。

有什么建议吗？

编辑:我希望最终产品是一个具有EGA/新值的向量/列。大概是这样的:

NA
11/13/12 21:00
11/13/12 20:50
11/13/12 07:15
11/13/12 10:18
11/13/12 10:25

Answer 1

这是一个端到端的解决方案:

##formats of the date-times
date.format <- "\\d{2}/\\d{2}/\\d{2} \\d{2}:\\d{2}"
##puts this together into a regex
regex.string <- paste0("EGA- (?:Old=",date.format," )?New=(",date.format,")")

##if pattern matches, get the part of "new" we are looking for
##otherwise NA
ifelse(grepl(regex.string,events5$data_updated),
  gsub(paste0("^.*",regex.string,".*$"),"\\1",events5$data_updated),
  NA_character_)

Answer 2

怎么样？

EGA-\s*(?:Old=\d{2}\/\d{2}\/\d{2}\s+\d{2}:\d{2}\s*)?New=(\d{2}\/\d{2}\/\d{2}\s+\d{2}:\d{2})

Answer 3

这里有一个替代方案，与@法老的正则表达式相比，它在< code > EGA -标签后有无限量的文本

/EGA-(?:(?!New=|").)+(New=[:\d\/ ]+)/g

如果否定前瞻中的“过于笼统，您可以将其更改为EGD。

演示说明:http://regex101.com/r/qY4uA0

如果不需要标志和分隔符，请将其删除。