R正则表达式可以替换开口支架而不是关闭支架

Question

I am trying to replace opening and closing brackets in a string. R seems to do it for the opening bracket:

> gsub("[\\[]","==","hello [world]")
[1] "hello ==world]"

but not for the closing brackets

> gsub("[\\]]","==","hello [world]")
[1] "hello [world]"

Why is this so?

Answer 1

Look, the pattern in gsub("[\\\\]]","==","hello\\\\] [world]") , [\\]] , is effectively matching a \\ followed with ] . Try gsub("[\\\\]]","==","hello\\\\] [world]") , and the result will be hello== [world] , the literal backslash will get replaced.

In a TRE regex pattern, a \\ inside a bracket expression matches a literal backslash.

As a fix for your "[\\\\]]" regex, you may remove the \\ from the pattern:

gsub("[[]","==","hello [world]")

See this R online demo .

You may escape it in a PCRE pattern though, as PCRE character classes allow escaped characters inside them:

gsub("[\\[]","==","hello [world]", perl=TRUE)

See another demo

If you need to replace either [ or ] , just put the ][ inside the bracket expression:

 gsub("[][]","==","hello [world]")

Answer 2

This simply works:

gsub("]", "==","hello [world]")
#"hello [world=="

Answer 3

A maybe more readable/straight forward way to do it is with stringi ,

library(stringi)
stri_replace_all_regex('hello [world]', '\\[|]', '==')
#[1] "hello ==world=="