如何提取模式"_"之间的子字符串和“."在R中 [英] How to extract substring between patterns "_" and "." in R

问题描述

我有很多文件名，如下所示:

I have many filenames which look like:

txt= "MA0051_IRF2.xml"

我要提取在"_"和."之间的IRF2.如何在R中执行此操作?

I want to extract IRF2 which is between "_" and ".". How do I do this in R?

推荐答案

要实现这一点，您需要一个正则表达式

To achieve this, you need a regexp that

• 匹配_前面的(可选)任意字符串:.*
• 匹配文字_:[_]
• 匹配直到(但不包括)next的所有内容.并将其存储在捕获组编号中. 1:([^.]+)
• 与文字匹配. :[.]
• 匹配后的(可选)任意字符串. :.*

• matches an (optional) arbitrary string in front of the _ : .*
• matches a literal _ : [_]
• matches everything up to (but not including) the next . and stores it in capturing group no. 1 : ([^.]+)
• matches a literal . : [.]
• matches an (optional) arbitrary string after the . : .*

然后在您致电gsub时，

In your call to gsub, you then

• 使用我们在上一步中构建的正则表达式
• 用第一个捕获组的内容替换整个字符串:\\1(我们需要转义反斜杠，因此要转义两个反斜杠)

• use the regular expression we built in the previous step
• replace the whole string with the contents of the first capturing group: \\1 (we need to escape the backslash, hence the double backslash)

示例:

gsub(".*[_]([^.]+)[.].*", "\\1", "MA0051_IRF2.xml")

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