How do I correctly reference a bracket within a character vector in R?

I am trying to access all the characters within a pair of brackets for some character vector (so that I can then reverse them). R doesn’t seem to be treating ")" the same as a normal character. I first tried:

solution <- function(inputString) {

  print(a <- unlist(strsplit(x=inputString,split="")))
  print(bracket.indices <- grep(pattern="(|)",x=a))

} 

I tried this with the following input string:

"(bar)"

What I’m wanting this bit of my code to do is simply give me the index number of the bracket characters so that I can later operate on the characters inside. I can’t manage it though. I run my code and I get:

[1] "(" "b" "a" "r" ")"
[1] 1 2 3 4 5

The first one is right. The second one not. I should have 1 and 5. Playing around a bit, I can see that something is going on with how R is taking the brackets. If I just my function to just have one bracket in grep:

solution <- function(inputString) {

  print(a <- unlist(strsplit(x=inputString,split="")))
  print(bracket.indices <- grep(pattern="(",x=a))
}

I get:

Error in grep(pattern = "(", x = a) : 
  invalid regular expression '(', reason 'Missing ')''
 In addition: Warning message:
In grep(pattern = "(", x = a) :
 Error in grep(pattern = "(", x = a) : 
invalid regular expression '(', reason 'Missing ')''

I thought, "OK, grep is a lost cause, so let me just play around with a for loop and see if I can do it that way, but that gives unlooked-for results as well:

solution <- function(inputString) {
  print(a <- unlist(strsplit(x=inputString,split="")))
  for (i in 1:length(a)) {
    if (a[i] == "(" | a[i] == ")") {
      bracket.indices <- which(a[i] == "(" | a[i] == ")")
    }

  print(bracket.indices)

  }
}

Result:

   solution("(bar)")
    [1] "(" "b" "a" "r" ")"
    [1] 1
    [1] 1
    [1] 1
    [1] 1
    [1] 1

I’ve been away from R for a while, and it shows. Any help guys?

>Solution :

We can add escape characters \\ to search specifically for ( or ).

solution <- function(inputString) {
  
  print(a <- unlist(strsplit(x=inputString,split="")))
  print(bracket.indices <- grep(pattern="\\(|\\)",x=a))
  
} 

Output

solution("(bar)")
# [1] "(" "b" "a" "r" ")"
# [1] 1 5