Recursive regex in R for curly braces

Question

I have some text string in the following pattern.

x = "sdfwervd \calculus{fff}{\trt{sdfsdf} & \trt{sdfsdf} & \trt{sdfsdf} \\{} sdfsdf & sdfsdf & sefgse3 } aserdd wersdf sewtgdf"

1. I want to use regex to capture the text "fff" in the string \calculus{fff} and replace it with something else.

2. Further I want to capture the string between the first { after \calculus{.+} and it's corresponding closing curly brace }.

How to do this with regex in R ?

The following captures everything till last curly brace.

gsub("(\\calculus\\{)(.+)(\\})", "", x)

Answer 1

For the second task you can use a recursive approach in combination with regmatches() and gregexpr() in base R:

x <- c("sdfwervd \\calculus{fff}{\\trt{sdfsdf} & \\trt{sdfsdf} & \\trt{sdfsdf} \\{} sdfsdf & sdfsdf & sefgse3 } aserdd wersdf sewtgdf")

pattern <- "\\{(?:[^{}]*|(?R))*\\}"
(result <- regmatches(x, gregexpr(pattern, x, perl = TRUE)))

---

This yields a list of the found submatches:

[[1]]
[1] "{fff}"                                                                          
[2] "{\\trt{sdfsdf} & \\trt{sdfsdf} & \\trt{sdfsdf} \\{} sdfsdf & sdfsdf & sefgse3 }"

See a demo for the expression on regex101.com.