Regex 如何从谷歌搜索结果页面URL中提取关键词？

我的数据集中的一个变量包含谷歌搜索结果页面的URL。我想从这些URL中提取搜索关键字

示例数据集：

keyw <- structure(list(user = structure(c(1L, 1L, 1L, 2L, 2L, 2L), .Label = c("p1", "p2"), class = "factor"),
                   url = structure(c(3L, 5L, 4L, 1L, 2L, 6L), .Label = c("https://www.google.nl/search?q=five+fingers&ie=utf-8&oe=utf-8&gws_rd=cr,ssl&ei=kERoVbmMO6fp7AaGioCYAw", "https://www.google.nl/search?q=five+fingers&ie=utf-8&oe=utf-8&gws_rd=cr,ssl&ei=kERoVbmMO6fp7AaGioCYAw#safe=off&q=five+short+fingers+", "https://www.google.nl/search?q=high+five&ie=utf-8&oe=utf-8&gws_rd=cr,ssl&ei=bENoVZSqL4ON7Qb5wIDIDg", "https://www.google.nl/search?q=high+five&ie=utf-8&oe=utf-8&gws_rd=cr,ssl&ei=bENoVZSqL4ON7Qb5wIDIDg#safe=off&q=high+five+with+a+chair", "https://www.google.nl/search?q=high+five&ie=utf-8&oe=utf-8&gws_rd=cr,ssl&ei=bENoVZSqL4ON7Qb5wIDIDg#safe=off&q=high+five+with+handshake", "https://www.youtube.com/watch?v=6HOallAdtDI"), class = "factor")), 
              .Names = c("user", "url"), class = "data.frame", row.names = c(NA, -6L))

此输出有三个问题：

我只需要这些词作为字符串。我需要的不是

q=high+five

，而是

high，five

如第2行、第3行和第5行所示，URL有时包含两个带有搜索关键字的部分。由于第一部分只是对前面搜索的引用，因此我只需要第二个搜索查询

当URL不是Google搜索页面URL时，它应该返回

NA

预期结果应为：

> keyw$words
[1] "high,five"                           
[2] "high,five,with,handshake"
[3] "high,five,with,a,chair"  
[4] "five,fingers"                        
[5] "five,short,fingers"
[6] NA

---

我该如何解决这个问题呢？

必须有一个更干净的方法，但可能类似于：

sapply(strsplit(keyw$words, "q="), function(x) {
  x <- if (length(x) == 2) x[2] else x[3]
  gsub("+", ",", gsub("\\+$", "", x), fixed = TRUE)
})
# [1] "high,five"                "high,five,with,handshake" "high,five,with,a,chair"  
# [4] "five,fingers"             "five,short,fingers" 

sapply（strsplit（keyw$words，“q=”），函数（x）{
x我想试试：

x<-as.character(keyw$url)
vapply(regmatches(x,gregexpr("(?<=q=)[^&]+",x,perl=TRUE)),
       function(y) paste(unique(unlist(strsplit(y,"\\+"))),collapse=","),"")
#[1] "high,five"                "high,five,with,handshake"
#[3] "high,five,with,a,chair"   "five,fingers"            
#[5] "five,fingers,short"

x更新（借用David的部分正则表达式）：

使用：

pat <- "^https://www\\.google.(?:com?.)?[a-z]{2,3}/.*\\b?q=([^&]*[^&+]).*"

产生：

[1] "high,five"                "high,five,with,handshake" "high,five,with,a,chair"  
[4] "five,fingers"             "five,short,fingers"       NA   

[1] "high,five"                "high,five,with,handshake" "high,five,with,a,chair"  
[4] "five,fingers"             "five,short,fingers,"     

在这里，我们使用贪婪来确保跳过所有内容直到最后一部分，然后使用标准的
子部分
/
\\1
技巧来捕获我们想要的内容。最后，将
+
替换为
，
或者这个

gsub("\\+", ",", gsub(".*q=([^&#]*[^+&]).*", "\\1", keyw$url))
# [1] "high,five"                "high,five,with,handshake" "high,five,with,a,chair"  
# [4] "five,fingers"             "five,short,fingers"  

评论后的另一个更新（看起来太复杂了，但这是我目前所能做到的最好的：）：


（查找
（？嗯…。这与我在聊天室中提出的建议类似，但不处理
，
end@DavidArenburg在过去的10分钟里没有出现在聊天室，是的，关于尾随逗号的观点很好。Thanx，尾随逗号需要删除。另请参阅我关于非谷歌的更新问题urls@Jaap，没问题，不过几乎可以肯定这是因为你有不同的谷歌网站。这只是特别匹配非常接近，也请参阅我在real上测试后更新的问题data@Jaap更新了答案，但我仍然想知道您希望通过
http://whatever.com/search?q=my+搜索+单词
应该是
NA
还是
my，search，words
？有趣的一点。如果我想给出
http://whatever.com/search?q=my+search+words
an
NA
value？@Jaap我在纯正则表达式中看不到任何方法。我将在今天晚些时候尝试使用双通过滤器更新此演变的答案。非常感谢！对于此特定问题，您的answer给了我想要的结果，因为我的数据集中只有谷歌搜索页面。对于未来，我肯定需要一个能够过滤掉特定搜索的解决方案（例如：所有像
http://google.com/search?q=my+搜索+单词
或特定页面上的所有搜索，如
http://whatever.com/search?q=my+搜索+单词
）Thanx。这是可行的，但其他解决方案确实更干净。另请参阅我关于谷歌的最新问题urls@Jaap，如果我没有弄错的话，我的代码也会给你你期望的
NA
——对吗？没错。我还在你的答案中包括了一个集成解决方案（可能会有所改进）。希望你不要介意。
[1] "high,five"                "high,five,with,handshake" "high,five,with,a,chair"  
[4] "five,fingers"             "five,short,fingers"       NA   

pat <- "^https://www\\.google.(?:com?.)?[a-z]{2,3}/.*\\b?q=([^&]*[^&+]).*"

gsub("\\+", ",", sub("^.*\\bq=([^&]*).*", "\\1", keyw$url))

[1] "high,five"                "high,five,with,handshake" "high,five,with,a,chair"  
[4] "five,fingers"             "five,short,fingers,"     

gsub("\\+", ",", gsub(".*q=([^&#]*[^+&]).*", "\\1", keyw$url))
# [1] "high,five"                "high,five,with,handshake" "high,five,with,a,chair"  
# [4] "five,fingers"             "five,short,fingers"  

keyw$words <- sapply(str_extract_all(str_extract(keyw$url,"https?:[/]{2}[^/]*google.*[/].*"),'(?<=q=|[+])([^$+#&]+)(?!.*q=)'),function(x) if(!length(x)) NA else paste(x,collapse=","))
> keyw$words
[1] "high,five"                "high,five,with,handshake" "high,five,with,a,chair"   "five,fingers"            
[5] "five,short,fingers"       NA             

> keyw$words <- sapply(str_extract_all(keyw$url,'(?:(?<=q=|\\+)([^$+#&]+)(?!.*q=))'),function(x) if(!length(x)) NA else paste(x,collapse=","))
> keyw$words
[1] "high,five"                "high,five,with,handshake" "high,five,with,a,chair"  
[4] "five,fingers"             "five,short,fingers"       NA