regex to replace text *outside* of {} - r

Question

I want to use regex to replace commands or tags around strings. My use case is converting LaTeX commands to bookdown commands, which means doing things like replacing \citep{*} with [#*], \ref{*} with \#ref(*), etc. However, lets stick to the generalized question:
Given a string <begin>somestring<end> where <begin> and <end> are known and somestring is an arbitrary sequence of characters, can we use regex to susbstitute <newbegin> and <newend> to get the string <newbegin>somestring<newend>?
For example, consider the LaTeX command \citep{bonobo2017}, which I want to convert to [#bonobo2017]. For this example:
<begin> = \citep{
somestring = bonobo2017
<end> = }
<newbegin> = [#
<newend> = ]
This question is basically the inverse of this question.
I'm hoping for an R or notepad++ solution.
Additional Examples
Convert \citet{bonobo2017} to #bonobo2017
Convert \ref{myfigure} to \#ref(myfigure)
Convert \section{Some title} to # Some title
Convert \emph{something important} to *something important*
I'm looking for a template regex that I can fill in my <begin>, <end>, <newbegin> and <newend> on a case-by-case basis.

Answer 1

You can try something like this with dplyr + stringr:
string = "\\citep{bonobo2017}"
begin = "\\citep{"
somestring = "bonobo2017"
end = "}"
newbegin = "[#"
newend = "]"
library(stringr)
library(dplyr)
string %>%
str_extract(paste0("(?<=\\Q", begin, "\\E)\\w+(?=\\Q", end, "\\E)")) %>%
paste0(newbegin, ., newend)
or:
string %>%
str_replace_all(paste0("\\Q", begin, "\\E|\\Q", end, "\\E"), "") %>%
paste0(newbegin, ., newend)
You can also make it a function for convenience:
convertLatex = function(string, BEGIN, END, NEWBEGIN, NEWEND){
string %>%
str_replace_all(paste0("\\Q", BEGIN, "\\E|\\Q", END, "\\E"), "") %>%
paste0(NEWBEGIN, ., NEWEND)
}
convertLatex(string, begin, end, newbegin, newend)
# [1] "[#bonobo2017]"
Notes:
Notice that I manually added an additional \ to "\\citep{bonobo2017}", this is because raw strings don't exist in R(I hope they do exist), so a single \ would be treated as an escape character. I need another \ to escape the first \.
The regex in str_extract uses positive lookbehind and positve lookahead to extract the somestring in between begin and end.
str_replace takes another approach of removing begin and end from string.
The "\\Q", "\\E" pair in the regex means "Backslash all nonalphanumeric characters" and "\\E" ends the expression. This is especially useful in your case since you likely have special characters in your Latex command. This expression automatically escapes them for you.