regex - 正则表达式不包括 R 中的单词

Question

我真的不知道如何在 R 中使用不匹配的正则表达式正确查找单词

例如:数据包括:

x =  c("hail", "small hail", "wind hail",  "deep hail",  "thunderstorm hail", "tstm wind hail", "gusty wind hail", "late season hail", "non severe hail", "marine hail")

我想找到所有有“冰雹”但没有“海洋”的观察者

我的尝试:

x[grep("[^(marine)] hail", x)]

-> 我只有 5 个:

"small hail"      "wind hail"       "deep hail"       "tstm wind hail"  "gusty wind hail"

不知道其他4个怎么样

Answer 1

使用环视断言。

> x =  c("hail", "small hail", "wind hail",  "deep hail",  "thunderstorm hail", "tstm wind hail", "gusty wind hail", "late season hail", "non severe hail", "marine hail")
> x[grep("^(?=.*hail)(?!.*marine)", x, perl=TRUE)]
[1] "hail"              "small hail"        "wind hail"        
[4] "deep hail"         "thunderstorm hail" "tstm wind hail"   
[7] "gusty wind hail"   "late season hail"  "non severe hail" 

或者

添加 \b必要时边界。 \b单词字符和非单词字符之间的匹配。

> x[grep("^(?=.*\\bhail\\b)(?!.*\\bmarine\\b)", x, perl=TRUE)]

^断言我们处于开始阶段。

(?=.*hail)正前瞻断言匹配必须包含字符串 hail

(?!.*marine)否定前瞻断言匹配将不包含字符串 marine .

因此，仅当两个条件都满足时，上面的正则表达式才会匹配起始 anchor 或行的开头。