gsub：如果没有用括号括起来，则替换单词

Question

I would like to gsub a word, but only cases where it is not wrapped in brackets.

x <- c("hello","[hello]")

I would like gsub(regex,"test",x) to return c("test","[hello]") , but I am having trouble creating the correct regex statement.

A naive implementation is: gsub("^(?!\\\\[).*$","test",x, perl=TRUE) , which works in the above case, but only because each string is one word, so it doesn't work for x <- "hello [hello]" for example, which I want to be test [hello] .

I've tried a bunch of different lookaheads to no avail. Any help would be appreciated.

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Input

x <- c("hello", "[hello]", "hello [hello]")

Desired

# [1] "test"         "[hello]"      "test [hello]"

Answer 1

You can use negative look around to set constraint to the word boundaries, for instance (?<!\\\\[)\\\\b\\\\w+\\\\b(?!\\\\]) will replace words only if the word boundary is not [] :

gsub("(?<!\\[)\\b\\w+\\b(?!\\])", "test", x, perl = TRUE)
# [1] "test [hello]"       # assuming this is your desired output

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\\\\b\\\\w+\\\\b will look for a word but with negative look-behind ?<! and negative look-ahead ?! , the word boundary should not be [] . You can also reference this answer .

Answer 2

We can do this easily with grep

x[grep("^[^[]+$", x)] <- "test"
x
#[1] "test"    "[hello]"

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Or with sub

sub("^[^[]+", "test", x)
#[1] "test"    "[hello]"

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For the second case

sub("^\\b[^[+]+\\b", "test", x1)
#[1] "test [hello]"

data

x <- c("hello","[hello]")
x1 <- "hello [hello]"