具有多个标准的r strsplit()

Question

我试图根据不同的标准来分割句子。我希望在“is”之后分几个句子，在“从不”之后再分几个句子。我能够根据这两种条件中的任何一种条件来拆分句子，但不能两者兼得。

str <- matrix(c("This is line one", "This is not line one", 
                "This can never be line one"), nrow = 3, ncol = 1)

>str
     [,1]                        
[1,] "This is line one"          
[2,] "This is not line one"      
[3,] "This can never be line one"

str2 <- apply(str, 1, function (x) strsplit(x, " is", fixed = TRUE))

> str2
[[1]]
[[1]][[1]]
[1] "This"      " line one"


[[2]]
[[2]][[1]]
[1] "This"          " not line one"


[[3]]
[[3]][[1]]
[1] "This can never be line one"

我想在“从不”之后把最后一句分开。我不知道该怎么做。

Answer 1

我们可以使用regex旁观者在“is”或“to”之后的空间分割行。在这里，(?<=\\bis)\\s+将is或|后面的一个或多个空格(\\s+)匹配为与“从不”字后面的空格(\\s+)匹配。

strsplit(str[,1], "(?<=\\bis)\\s+|(?<=\\bnever)\\s+", perl = TRUE)
#[[1]]
#[1] "This is"  "line one"

#[[2]]
#[1] "This is"      "not line one"

#[[3]]
#[1] "This can never" "be line one"   

如果我们想移除“is”和“never”

strsplit(str[,1], "(?:\\s+(is|never)\\s+)")
#[[1]]
#[1] "This"     "line one"

#[[2]]
#[1] "This"         "not line one"

#[[3]]
#[1] "This can"    "be line one"