add exclude arg to half_slashes

Author: AdamSpannbauer

r_regex_tester/helper_functions.R

@@ -1,6 +1,21 @@
 library(data.table)
 
-half_slashes = function(str) {
+
+half_slashes = function(str, exclude = character(0)) {
+  #' Given a string, remove half of the escaping backslashes
+  #'
+  #' @param str A string to remove backslashes from
+  #' @param exclude A character vector of items to exclude from processing
+  #'
+  #' @return A version of the input string with half of the escaping chars
+  #' 
+  #' @details An exception will be thrown if removing slashes leads to a parsing
+  #'         error.  For example, "\\" will be converted to "\" which is not
+  #'         a valid string.
+  #'
+  #' @examples
+  #' half_slashes("\\\\")
+  #' # [1] "\\"
   deparsed = deparse(str)
 
   half_df = data.table::as.data.table(
@@ -13,9 +28,14 @@ half_slashes = function(str) {
   half_df[, out := paste0(half_slash, char_cap)]
   half_df = unique(half_df[order(nchar(out)), ])
 
-  # Removing slashes before double quoutes breaks eval
+  # Removing slashes before double quotes breaks eval
   half_df = half_df[char_cap != '"']
 
+  # Dirty fix for new lines...
+  for (x in exclude) {
+    half_df[match == x, out := x]
+  }
+  
   halfed_deparse = mgsub(half_df$match,
                          half_df$out,
                          deparsed,