feat(list): adding list:median

Author: SuperFola

List.ark

@@ -201,7 +201,24 @@
     (set _index (+ 1 _index)) })
   _output }))
 
-(import std.Math :min :max)
+(import std.Math :min :max :even)
+
+# @brief Find the median in a list of numbers
+# @param _L list of numbers
+# @details The original list is not modified.
+# =begin
+# (let value (list:median [0 1 2 3 5 8]))  # 2.5
+# =end
+# @author https://github.com/SuperFola
+(let median (fun ((ref _L)) {
+  (let _n (len _L))
+  (if (= 0 _n)
+    nil
+    {
+      (let _s (sort _L))
+      (if (math:even _n)
+        (/ (+ (@ _s (- (/ _n 2) 1)) (@ _s (/ _n 2))) 2)
+        (@ _s (/ _n 2))) }) }))
 
 # @brief Drop the first n elements of a list
 # @param _L the list to work on

tests/list-tests.ark

@@ -64,6 +64,14 @@
         (test:eq (list:max b) 6)
         (test:eq (list:max [-1]) -1) })
 
+    (test:case "median" {
+        (test:eq (list:median []) nil)
+        (test:eq (list:median [1]) 1)
+        (test:eq (list:median [1 2]) 1.5)
+        (test:eq (list:median [2 1 3]) 2)
+        (test:eq (list:median [1 2 2 1]) 1.5)
+        (test:eq (list:median [1 2 2 1 3]) 2) })
+
     (test:case "drop" {
         (test:eq (list:drop a 0) [1 2 3])
         (test:eq (list:drop a 1) [2 3])