R中的gsub和regex遇到问题 [英] Trouble with gsub and regex in R

问题描述

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，此代码工作正常，但当括号中的数字较大时，则无效.

---

这会产生错误:

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 {}'

解决方案

背景

R gsub默认情况下使用TRE正则表达式库.限制量词中的边界从0到TRE代码中定义的RE_DUP_MAX有效.请参阅此TRE参考:

绑定 是以下其中之一，其中n和m是0和RE_DUP_MAX

之间的无符号十进制整数

RE_DUP_MAX似乎设置为255(请参见 TRE源文件显示#define RE_DUP_MAX 255)，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风味，添加perl = TRUE，它将起作用.

R演示:

> 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"

I am using gsub in R to add text into the middle of a string. It works perfectly but for some reason, when the location gets too long it throws an error. The code is below:

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 {}'

This code works fine when the number in the brackets(273 in this case) is less but not when it is this large.

---

This produces the error:

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 {}'

解决方案

Background

R gsub uses TRE regex library by default. The boundaries in the limiting quantifier are valid from 0 till RE_DUP_MAX that is defined in the TRE code. See this TRE reference:

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

It seems that the RE_DUP_MAX is set to 255 (see this TRE source file showing #define RE_DUP_MAX 255), and thus, you cannot use more in {n,m} limiting quantifier.

Solution

Use PCRE regex flavor, add perl = TRUE and it will work.

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"

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