regex - R中的gsub和regex遇到问题

Question

我在R中使用gsub将文本添加到字符串的中间。它可以完美工作，但是由于某些原因，当位置太长时会引发错误。代码如下:

gsub(paste0('^(.{', as.integer(loc[1])-1, '})(.+)$'), new_cols, sql)

Error in gsub(paste0("^(.{273})(.+)$"), new_cols, sql) :  invalid
  regular expression '^(.{273})(.+)$', reason 'Invalid contents of {}'

当括号中的数字较小(在这种情况下为273)时，此代码运行良好，但当括号中的数字较大时，此代码则无法正常工作。

这将产生错误:

sql <- "The cat with the bat went to town. He ate the fat mat and wouldn't stop til the sun came up. He was a fat cat that lived with a rat who owned many hats.The cat with the bat went to town. He ate the fat mat and wouldn't stop til the sun came up. He was a fat cat that lived with a rat who owned many hats."  
new_cols <- "happy" 
gsub('^(.{125})(.+)$', new_cols, sql)  #**Works
gsub('^(.{273})(.+)$', new_cols, sql) 

Error in gsub("^(.{273})(.+)$", new_cols, sql) :    invalid regular
  expression '^(.{273})(.+)$', reason 'Invalid contents of {}'

Answer 1

背景
R gsub默认使用TRE regex库。限制量词中的边界从0到TRE代码中定义的RE_DUP_MAX都是有效的。参见this TRE reference:

A bound is one of the following, where n and m are unsigned decimal integers between 0 and RE_DUP_MAX

似乎 RE_DUP_MAX设置为255(请参见显示 #define RE_DUP_MAX 255的此 TRE source file)，因此，您不能在 {n,m}限制量词中使用更多内容。
解决方案
使用PCRE regex风格，添加 perl = TRUE，它将起作用。
R demo:

> sql <- "The cat with the bat went to town. He ate the fat mat and wouldn't stop til the sun came up. He was a fat cat that lived with a rat who owned many hats.The cat with the bat went to town. He ate the fat mat and wouldn't stop til the sun came up. He was a fat cat that lived with a rat who owned many hats."
> new_cols <- "happy"
> gsub('^(.{273})(.+)$', new_cols, sql, perl=TRUE)
[1] "happy"