From 9c7e0cc714eceef729febe42d5816e749d54353d Mon Sep 17 00:00:00 2001
From: Martin Chan <martinchan53@gmail.com>
Date: Tue, 16 Apr 2024 17:10:41 +0100
Subject: [PATCH] feat: add `before` argument

---
 R/subset_from_match.R | 37 +++++++++++++++++++++++++------------
 1 file changed, 25 insertions(+), 12 deletions(-)

diff --git a/R/subset_from_match.R b/R/subset_from_match.R
index a3d4055..b6f657c 100644
--- a/R/subset_from_match.R
+++ b/R/subset_from_match.R
@@ -1,24 +1,37 @@
 #' @title Subset a List from a Matched String
-#' 
-#' @description
-#' This function takes a list of strings and a key string as input. It returns a new list that starts from the first occurrence of the key string in the original list and includes all the strings that follow it. If the key string is not found in the list, the function returns `NULL`.
-#' 
+#'
+#' @description This function takes a list of strings and a key string as input.
+#'   It returns a new list that starts from the first occurrence of the key
+#'   string in the original list and includes all the strings that follow it. If
+#'   the key string is not found in the list, the function returns `NULL`.
+#'   Optional argument `before` allows the logic to be reversed, returning a new
+#'   list that start from the first value in the original list up to the matched
+#'   string.
+#'
 #' @param x A character vector to perform the matching and subsetting on.
 #' @param key A character string to match in `x`.
-#' 
-#' @return A character vector starting from the first occurrence of `key` in `x` and including all subsequent elements. If `key` is not found in `x`, the function returns `NULL`.
-#' 
+#' @param before A logical value indicating whether the strings _before_ the
+#'   matched key should be returned. Defaults to FALSE. If set to TRUE, strings
+#'   _before_ the matched key are returned.
+#'
+#' @return By default, a character vector starting from the first occurrence of
+#'   `key` in `x` and including all subsequent elements. Logic can be reversed
+#'   with `before` argument. If `key` is not found in `x`, the function returns
+#'   `NULL`.
+#'
 #' @examples
 #' x <- c("a", "b", "c", "d", "e")
 #' key <- "c"
 #' subset_from_match(x, key)  # Returns: "c" "d" "e"
-#' 
+#'
 #' @export
-subset_from_match <- function(x, key) {
+subset_from_match <- function(x, key, before = FALSE) {
   index <- match(key, x)
-  if (!is.na(index)) {
-    return(x[index:length(x)])
+  if (!is.na(index) & !before) {
+    x[index:length(x)]
+  } else if (!is.na(index) & before){  
+    x[1:index] # up to the matched key
   } else {
-    return(NULL)
+    NULL
   }
 }