如何使用grep()来查找完全匹配 [英] How to use grep() to find exact match
本文介绍了如何使用grep()来查找完全匹配的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
string = c(apple,apples,applez)
grep(apple,string)
这将为我提供 string
中所有三个元素的索引。但我想要一个完全匹配的单词苹果(即我只想 grep()
返回索引1)。
解决方案
使用单词边界 \ b
和非单词字符,
string = c(apple,apples,applez)
grep(\\\\ bapple \\b,string)
[1] 1
OR
使用锚点。 ^
声明我们正处于开始阶段。 $
断言我们在最后。
grep(^ apple $,string)
[1] 1
您可以将正则表达式存储在
pat < - \\bapple\\
grep(pat,string)
[1] 1
pat < - ^ apple $
grep(pat,string)
[1] 1
更新:
paste(^,pat,$,sep =)
[1]^ apple $
string
[1]appleapple:s (^,pat,$,sep =),字符串)
[ 1] 1
string = c("apple", "apples", "applez")
grep("apple", string)
This would give me the index for all three elements in string
. But I want an exact match on the word "apple" (i.e I just want grep()
to return index 1).
解决方案
Use word boundary \b
which matches a between a word and non-word character,
string = c("apple", "apples", "applez")
grep("\\bapple\\b", string)
[1] 1
OR
Use anchors. ^
Asserts that we are at the start. $
Asserts that we are at the end.
grep("^apple$", string)
[1] 1
You could store the regex inside a variable and then use it like below.
pat <- "\\bapple\\b"
grep(pat, string)
[1] 1
pat <- "^apple$"
grep(pat, string)
[1] 1
Update:
paste("^",pat,"$", sep="")
[1] "^apple$"
string
[1] "apple" "apple:s" "applez"
pat
[1] "apple"
grep(paste("^",pat,"$", sep=""), string)
[1] 1
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