R: Hep with regex！- ^、|、\\、_和$的组合

Question

下面是我的R对象(x)和一些可以工作的命令和一些不能工作的命令。

(x <- c("q10_1", "q10_2", "q10_11", "q12_1", "q12_2", "q13_1", "q13_11"))

# Which strings start with "q10" or "q12? - WORKS
x[grep("^q10|q12", x)]

# Which strings end with "1"? - WORKS
x[grep("1$", x)]

# Which strings end with "_1"? - WORKS
x[grep("\\_1$", x)]

# Which strings start with "q10" AND contain a "1"? - WORKS
x[grep("^q10.+1", x)]

# Which strings start with "q10" AND end with a "_1"? - DOES NOT WORK
x[grep("^q10.+\\_1$", x)]

# Which strings start with "q10" or "q12 AND end with "_1"? - WORKS INCORRECTLY
x[grep("^q10|q12.+\\_1$", x)]

谢谢!

Answer 1

下面是所有的修复和优化：

x <- c("q10_1", "q10_2", "q10_11", "q12_1", "q12_2", "q13_1", "q13_11")
## Which strings start with "q10" or "q12? - WORKS - FIXED
x[grep("^q1[02]", x)]
## Which strings end with "1"? - WORKS
x[grep("1$", x)]
## Which strings end with "_1"? - WORKS - FIXED
x[grep("_1$", x)]
## Which strings start with "q10" AND contain a "1"? - WORKS - FIXED
x[grep("^q10.*1", x)]
## Which strings start with "q10" AND end with a "_1"? - DOES NOT WORK - FIXED
x[grep("^q10.*_1$", x)]
## Which strings start with "q10" or "q12 AND end with "_1"? - WORKS INCORRECTLY - FIXED
x[grep("^q1[02].*_1$", x)]

请参阅IDEONE demo

备注：

可以将

• ^q10|q12表示为^q1[02]，以提高性能并缩短模式。这也解决了你在input.
• \\_1$中任何地方匹配q12时遇到的^q10|q12问题-你不需要转义q10
• Same -你需要使用一个*量词，因为在^q10|q12后面可以有*，就像上面最后两个表达式的问题一样。*匹配0个或更多字符，而+需要至少1个字符。因此，您没有匹配项。
• 最后一个- ^q10|q12.+\\_1$ -匹配开头的q10，结尾的q12.+_1，逻辑由于缺少分组(^(q10|q12).+\\_1$)而被破坏，但最好使用^q1[02].*_1$.