fix Median operation returns incorrect result for unsorted odd-length inputs (#2284)

src/core/lib/Arithmetic.mjs

@@ -108,14 +108,17 @@ export function mean(data) {
  * @returns {BigNumber}
  */
 export function median(data) {
-    if ((data.length % 2) === 0 && data.length > 0) {
+    if (data.length > 0) {
         data.sort(function(a, b) {
             return a.minus(b);
         });
-        const first = data[Math.floor(data.length / 2)];
+
-        const second = data[Math.floor(data.length / 2) - 1];
+        if ((data.length % 2) === 0) {
-        return mean([first, second]);
+            const first = data[Math.floor(data.length / 2)];
-    } else {
+            const second = data[Math.floor(data.length / 2) - 1];
+            return mean([first, second]);
+        }
+
         return data[Math.floor(data.length / 2)];
     }
 }

tests/operations/tests/Median.mjs

@@ -0,0 +1,33 @@
+/**
+ * Median operation tests.
+ *
+ * @author copilot-swe-agent[bot]
+ * @copyright Crown Copyright 2018
+ * @license Apache-2.0
+ */
+import TestRegister from "../../lib/TestRegister.mjs";
+
+TestRegister.addTests([
+    {
+        name: "Median: odd-length input",
+        input: "10 1 2",
+        expectedOutput: "2",
+        recipeConfig: [
+            {
+                op: "Median",
+                args: ["Space"],
+            },
+        ],
+    },
+    {
+        name: "Median: even-length input",
+        input: "10 1 2 5",
+        expectedOutput: "3.5",
+        recipeConfig: [
+            {
+                op: "Median",
+                args: ["Space"],
+            },
+        ],
+    },
+]);