正则表达式：获取最靠近另一个模式左侧的模式之间的文本

Question

我有一个字符串 txt，其中包括模式 John 和几个国家。我还有 vec_regex，一堆匹配国家的正则表达式（但不是所有在文本中提到的）。

我想得到的是最靠近约翰左边的匹配国家和约翰之间的文本：法国文本约翰。

我认为这是需要的负面前瞻，但我无法让它工作。（参见 here and here）。非常感谢！

library(stringr)
txt <- "Germany Russia and Germany Russia text Germany text France text John text text France and Spain"

vec_regex <- c("German\w*", "France|French", "Spain|Spanish", "Russia\w*")
vec_regex_or <- paste(vec_regex, collapse="|")
vec_regex_or
#> [1] "German\w*|France|French|Spain|Spanish|Russia\w*"

pattern_left <- paste0("(",vec_regex_or, ")",".*John")
pattern_left
#> [1] "(German\w*|France|French|Spain|Spanish|Russia\w*).*John"
str_extract(txt, regex(pattern_left))
#> [1] "Germany Russia and Germany Russia text Germany text France text John"

pattern_left <- paste0("(",vec_regex_or, ")","(?!(",vec_regex_or,"))",".*John") #neg. lookahead
pattern_left
#> [1] "(German\w*|France|French|Spain|Spanish|Russia\w*)(?!(German\w*|France|French|Spain|Spanish|Russia\w*)).*John"
str_extract(txt, regex(pattern_left))
#> [1] "Germany Russia and Germany Russia text Germany text France text John"

^{由 reprex package (v2.0.1)}

于 2021-12-30 创建

Answer 1

你需要使用

pattern_left <- paste0("(",vec_regex_or, ")","(?:(?!",vec_regex_or,").)*","John")
pattern_left
# => [1] "(German\w*|France|French|Spain|Spanish|Russia\w*)(?:(?!German\w*|France|French|Spain|Spanish|Russia\w*).)*John"
str_extract(txt, regex(pattern_left))
# => [1] "France text John"

"(?:(?!",vec_regex_or,").)*" 部分正确创建了。

此外，如果您打算将这些字符串作为整个单词进行匹配，请考虑添加单词边界：

pattern_left <- paste0("\b(",vec_regex_or, ")\b","(?:(?!",vec_regex_or,").)*","John\b")

正则表达式：获取最靠近另一个模式左侧的模式之间的文本

regex: get text between pattern nearest to the left of another pattern

r

regex

stringr