使用模式进行部分字符串匹配 [英] Partial string matching using patterns

问题描述

我需要在 R 中编写一个查询来匹配列名中的部分字符串.我正在寻找类似于 SQL 中的 LIKE 运算符的东西.例如，如果我知道字符串的开头、中间或结尾部分，我会以以下格式编写查询:

I need to write a query in R to match partial string in column names. I am looking for something similar to LIKE operator in SQL. For e.g, if I know beginning, middle or end part of the string I would write the query in format:

LIKE 'beginning%middle%' 

在 SQL 中，它将返回匹配的字符串.在 pmatch 或 grep 中，我似乎只能指定 'beginning' 、 'end' 而不是顺序.我正在寻找的 R 中是否有类似的功能?

in SQL and it would return matching strings. In pmatch or grep it seems I can only specify 'beginning' , 'end' and not the order. Is there any similar function in R that I am looking for?

例如，假设我正在寻找向量:

For example, say I am looking in the vector:

y <- c("I am looking for a dog",
       "looking for a new dog", "a dog", "I am just looking")

假设我想编写一个查询，它选择 寻找新狗" 并且我知道字符串的开头是 "looking" 并且字符串的结尾是狗".如果我执行 grep("dog",y) 它将返回 1,2,3.有什么办法可以在 grep 中指定开始和结束?

Let's say I want to write a query which picks "looking for a new dog" and I know start of the string is "looking" and end of string is "dog". If I do a grep("dog",y) it will return 1,2,3. Is there any way I can specify beginning and end in grep?

推荐答案

grep 函数支持正则表达式，有了正则表达式，你几乎可以匹配任何东西

The grep function supports regular expressions and with regular expressions, you can match almost anything

y<- c("I am looking for a dog", "looking for a new dog", "a dog", "I am just looking")
grep("looking.*dog",y, value=T)
# [1] "I am looking for a dog" "looking for a new dog" 

这里这个模式先寻找looking，然后是maybe something"，然后是dog.所以这应该做你想做的.

Here this pattern looks for looking then "maybe something" then dog. So that should do what you want.

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