NOT-A-STUDENT-PR: Update Solution and tests for Sprint 1 'fix median' task

Sprint-1/fix/median.js

@@ -11,18 +11,33 @@
 // }
 
 // Explanation:
-// .splice() is a mutating method, so it updates the array in place.
-// to prevent this, you could take a copy of the array and use .splice(),
-// or you could use bracket notation to element at the desired index
+// The original implementation has several mistakes:
+// 1 - .splice() mutates or changes the original array. We don't want this to happen.
+// 2 - We actually don't need .splice() or any other method to find a median.
+// 3 - We must sort the array before we search for the median.
+// 4 - We should check if the 'list' parameter actually has numbers, otherwise try to filter
+// out all non-numeric values and throw an error or return null if there are no numeric values.
 
-function calculateMedian(list) {
-  const middleIndex = Math.floor(list.length / 2);
 
-  if (list.length % 2 === 0) { // use the remainder operator (%) to check if the array length is even
-    return (list[middleIndex - 1] + list[middleIndex]) / 2;
+// Example of a function calculating median and returning null in case no numeric values provided.
+
+function calculateMedian(list) {
+  if (!Array.isArray(list)) {
+    return null;
   }
+  const onlyNumberList = list.filter(item => typeof item === 'number' && !isNaN(item));
 
-  return list[middleIndex];
+  if (!onlyNumberList.length) {
+    return null;
+  } else {
+    const sortedList = onlyNumberList.sort((current, next) => current - next);
+    const indexNearMiddleOfArray = Math.floor(sortedList.length / 2);
+    if (sortedList.length % 2 === 0) {
+      return (sortedList[indexNearMiddleOfArray - 1] + sortedList[indexNearMiddleOfArray]) / 2;
+    } else {
+      return sortedList[indexNearMiddleOfArray];
+    }
+  }
 }
 
 module.exports = calculateMedian;

Sprint-1/fix/median.test.js

@@ -7,20 +7,42 @@
 const calculateMedian = require("./median.js");
 
 describe("calculateMedian", () => {
-  it("returns the median for odd length array", () => {
-    expect(calculateMedian([1, 2, 3])).toEqual(2);
-    expect(calculateMedian([1, 2, 3, 4, 5])).toEqual(3);
-  });
+  [
+    { input: [1, 2, 3], expected: 2 },
+    { input: [1, 2, 3, 4, 5], expected: 3 },
+    { input: [1, 2, 3, 4], expected: 2.5 },
+    { input: [1, 2, 3, 4, 5, 6], expected: 3.5 },
+  ].forEach(({ input, expected }) =>
+    it(`returns the median for [${input}]`, () => expect(calculateMedian(input)).toEqual(expected))
+  );
 
-  it("returns the average of middle values for even length array", () => {
-    expect(calculateMedian([1, 2, 3, 4])).toEqual(2.5);
-    expect(calculateMedian([1, 2, 3, 4, 5, 6])).toEqual(3.5);
-  });
+  [
+    { input: [3, 1, 2], expected: 2 },
+    { input: [5, 1, 3, 4, 2], expected: 3 },
+    { input: [4, 2, 1, 3], expected: 2.5 },
+    { input: [6, 1, 5, 3, 2, 4], expected: 3.5 },
+  ].forEach(({ input, expected }) =>
+    it(`returns the correct median for unsorted array [${input}]`, () => expect(calculateMedian(input)).toEqual(expected))
+  );
 
-  it("doesn't modify the input", () => {
+  it("doesn't modify the input array [1, 2, 3]", () => {
     const list = [1, 2, 3];
     calculateMedian(list);
-
     expect(list).toEqual([1, 2, 3]);
   });
-});
+
+  [ 'not an array', 123, null, undefined, {}, [], ["apple", null, undefined] ].forEach(val =>
+    it(`returns null for non-numeric array (${val})`, () => expect(calculateMedian(val)).toBe(null))
+  );
+
+  [
+    { input: [1, 2, "3", null, undefined, 4], expected: 2 },
+    { input: ["apple", 1, 2, 3, "banana", 4], expected: 2.5 },
+    { input: [1, "2", 3, "4", 5], expected: 3 },
+    { input: [1, "apple", 2, null, 3, undefined, 4], expected: 2.5 },
+    { input: [3, "apple", 1, null, 2, undefined, 4], expected: 2.5 },
+    { input: ["banana", 5, 3, "apple", 1, 4, 2], expected: 3 },
+  ].forEach(({ input, expected }) =>
+    it(`filters out non-numeric values and calculates the median for [${input}]`, () => expect(calculateMedian(input)).toEqual(expected))
+  );
+});