在 R 正则表达式中使用九个以上的反向引用

发布于 2024-12-18 17:04:52 字数 341 浏览 2 评论 0原文

下面的代码不起作用，因为无法正确读取 \10、\11 等的替换字符串。它会将 \10 读作 \1 并打印 0，你能帮我解决这个问题吗？其中一个线程中有一个答案，说我应该使用捕获或命名组，但我真的不明白如何使用它们。

headline <- gsub("regexp with 10 () brackets",
"\\1 ### \\2 ### \\3 ### \\4 ### \\5 ### \\6 ### \\7 ### \\8 ### \\9 ###
\\10### \\11### \\12### \\13### \\14### \\15### \\16",
page[headline.index])

原文

The code below does not work, because the replacement string for \10, \11, and so on, cannot be read properly. It reads \10 as \1 and print 0 instead, can you help me fix it?
There is an answer in one of the threads, saying that I am supposed to use capturing or naming groups, but I don't really understand how to use them.

headline <- gsub("regexp with 10 () brackets",
"\\1 ### \\2 ### \\3 ### \\4 ### \\5 ### \\6 ### \\7 ### \\8 ### \\9 ###
\\10### \\11### \\12### \\13### \\14### \\15### \\16",
page[headline.index])

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乖乖兔^ω^ 2024-12-25 17:04:52

根据 ?regexp，自 R-2.14.0 起，命名捕获已在 regexpr() 和 gregexpr() 中可用。不幸的是，它还不能用于 sub()，或者事实证明，gsub()。因此，它可能对您仍然有用，但可能需要比您希望的更多的跑腿工作。

（有关命名组的一些示例，请参阅 ?regexpr 的示例部分。）

稍后添加，遵循 GREG SNOW 的答案

Greg Snow 暗示了这样做的可能性使用 gsubfn 包。下面的示例显示 gsubfn() 确实可以处理超过九个反向引用：

require(gsubfn)
string <- "1:2:3:4:5:6:7:8:9:10:11"
pat <- "^(\\d)+:(\\d)+:(\\d)+:(\\d)+:(\\d)+:(\\d)+:(\\d)+:(\\d)+:(\\d)+:(\\d)+:(\\d)+"
gsubfn(pat, ~ paste(a,b,c,d,e,f,g,h,i,j,k,j,i,h,g,f,e,d,c,e,a), string)  
# [1] "1 2 3 4 5 6 7 8 9 10 11 10 9 8 7 6 5 4 3 5 1"

According to ?regexp, named capture has been available in regexpr() and gregexpr() since R-2.14.0. Unfortunately, it is not yet available for sub() or, it turns out, gsub(). So, it may still be useful to you, but will probably require a bit more legwork than you might have hoped.

(For a few examples of naming groups in action, see the examples section of ?regexpr.)

ADDED LATER, FOLLOWING GREG SNOW'S ANSWER

Greg Snow alluded to the possibility of doing this with the gsubfn package. Here's an example that shows that gsubfn() can indeed handle more than nine backreferences:

require(gsubfn)
string <- "1:2:3:4:5:6:7:8:9:10:11"
pat <- "^(\\d)+:(\\d)+:(\\d)+:(\\d)+:(\\d)+:(\\d)+:(\\d)+:(\\d)+:(\\d)+:(\\d)+:(\\d)+"
gsubfn(pat, ~ paste(a,b,c,d,e,f,g,h,i,j,k,j,i,h,g,f,e,d,c,e,a), string)  
# [1] "1 2 3 4 5 6 7 8 9 10 11 10 9 8 7 6 5 4 3 5 1"

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