在R中的字符串后提取一定数量的单词或特殊字符

我试图在特定字符串后提取一定数量的单词

library(stringr)

x <- data.frame(end = c("source: from animal origin as Vitamin A / all-trans-Retinol: Fish in general, liver and dairy products;", "source: Eggs, liver, certain fish species such as sardines, certain mushroom species such as shiitake", "source: Leafy green vegetables such as spinach; egg yolks; liver"))

不管它是否将/和-算作单词，因为我总是可以将量词的数量调整为更多（在我的情况下，我不介意提取比我需要的更多的量词）

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谢谢

我们可以用

{4,8}

trimws(stringr::str_extract(x$end, '(?<=source:\\s)(\\w+,?\\s){4,8}'))

问题是：是否有一个正则表达式包含特殊字符（或绕过它们），这样我仍然可以提取所需的单词？我注意到其他字符（例如-）或双空格也会出现同样的情况

边节点：这是一种XY问题（）

你的问题不是，正则表达式不起作用-你的问题是正则表达式起作用了，但你期望一些不同的东西。您可以使用它来选择特定字符串后面的8个单词，但非单词（

/

）前面只有6个单词，因此这与您的模式不匹配

因此，为了给你的问题提供一个“答案”，你应该首先重做你的问题：

你的确切期望是什么

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akrun的解决方案可以匹配4-8个单词中的任何一个，但怀疑这是您真正需要的。

这里有一个使用

regmatches

+

gsub

lapply(regmatches(u <- gsub(".*?source:\\s+?","",x$end),gregexpr("\\w+",u)),`[`,1:4)

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您可以依赖与任何非空白字符匹配的

\S

速记字符类：

(?<=source:\s)\S+(?:\s+\S+){3,7}\b

输出：

[1] "from animal origin as Vitamin A / alltrans-Retinol"
[2] "Eggs, liver, certain fish species such as sardines"
[3] "Leafy green vegetables such as spinach; egg yolks" 

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也许您需要

”（？谢谢。是的，我应该添加预期结果以澄清我的问题（现在添加）。尝试跳过非单词（如果有正则表达式）。或要提取特殊字符并继续提取后面的内容，例如\\w包含任何字母表，是否有其他正则表达式包含任何字母表或特殊字符？
pat <- sprintf('(?<=source:\\s)(\\w+,?\\s){%d}', c(8, 4))

library(dplyr)
do.call(coalesce, lapply(pat, function(y) trimws(stringr::str_extract(x$end, y))))
#[1] "from animal origin as"     
#[2] "Eggs, liver, certain fish species such as sardines,"
#[3] "Leafy green vegetables such"  

lapply(regmatches(u <- gsub(".*?source:\\s+?","",x$end),gregexpr("\\w+",u)),`[`,1:4)

[[1]]
[1] "from"   "animal" "origin" "as"

[[2]]
[1] "Eggs"    "liver"   "certain" "fish"

[[3]]
[1] "Leafy"      "green"      "vegetables" "such"

(?<=source:\s)\S+(?:\s+\S+){3,7}\b

library(stringr)
x <- data.frame(end = c("source: from animal origin as Vitamin A / alltrans-Retinol: Fish in general, liver and dairy products;", "source: Eggs, liver, certain fish species such as sardines, certain mushroom species such as shiitake", "source: Leafy green vegetables such as spinach; egg yolks; liver"))
stringr::str_extract(x$end, "(?<=source:\\s)\\S+(?:\\s+\\S+){3,7}\\b")

[1] "from animal origin as Vitamin A / alltrans-Retinol"
[2] "Eggs, liver, certain fish species such as sardines"
[3] "Leafy green vegetables such as spinach; egg yolks"