From 31ccdbf38f27546253ec4c1f4815d28319829124 Mon Sep 17 00:00:00 2001
From: Justin Zou <justclaner@gmail.com>
Date: Sat, 13 Jul 2024 18:00:13 -0400
Subject: [PATCH] feat: StandardDeviation algorithm for Math

---
 Maths/StandardDeviation.js           | 34 ++++++++++++++++++++++++++++
 Maths/test/StandardDeviation.test.js | 32 ++++++++++++++++++++++++++
 2 files changed, 66 insertions(+)
 create mode 100644 Maths/StandardDeviation.js
 create mode 100644 Maths/test/StandardDeviation.test.js

diff --git a/Maths/StandardDeviation.js b/Maths/StandardDeviation.js
new file mode 100644
index 0000000000..34dc1fa14b
--- /dev/null
+++ b/Maths/StandardDeviation.js
@@ -0,0 +1,34 @@
+
+/* 
+ * Returns the standard deviation given an array of integers
+ * @param  int[]   nums    array of integers
+ * @return int             standard deviation              
+ * @see https://en.wikipedia.org/wiki/Standard_deviation
+ */
+function standardDeviation(nums) {
+
+    if (nums.length < 2) {
+        throw new Error("At least two numbers in input array are required!");
+    }
+    if (!Array.isArray(nums)) {
+        throw new TypeError("Array required!");
+    }
+
+    let sum = 0;
+    for (let i = 0; i < nums.length; i++) {
+        if (!Number.isInteger(nums[i])) {
+            throw new TypeError("Integer type required in array input!");
+        }
+        sum += nums[i];
+    }
+    let avg = sum/nums.length;
+    let deviationSquareSum = 0;
+    for (let i = 0; i < nums.length; i++) {
+        let square = Math.pow((nums[i]-avg),2);
+        deviationSquareSum += square;
+    }
+   
+    return(Math.sqrt(deviationSquareSum/nums.length));
+}
+
+export {standardDeviation}
\ No newline at end of file
diff --git a/Maths/test/StandardDeviation.test.js b/Maths/test/StandardDeviation.test.js
new file mode 100644
index 0000000000..e62f4492e2
--- /dev/null
+++ b/Maths/test/StandardDeviation.test.js
@@ -0,0 +1,32 @@
+import { standardDeviation } from "../StandardDeviation.js";
+
+test("Calculate STD of 3,5,6,10,23,12,19", ()=>{
+    expect(standardDeviation([3,5,6,10,23,12,19])).toBeCloseTo(6.9164105353773);
+})
+
+test("Calculate STD of -2,-5,1,12,23,-81,-23", () => {
+    expect(standardDeviation([-2,-5,1,12,23,-81,-23])).toBeCloseTo(31.598889156399);
+})
+
+test("Calculate STD of 0,0,0", () => {
+    expect(standardDeviation([0,0,0])).toBeCloseTo(0);
+})
+
+test("Calculate STD of -7,7", () => {
+    expect(standardDeviation([-7,7])).toBeCloseTo(7);
+})
+
+test("Throw error - array has less than two items", () => {
+    expect(() => standardDeviation([])).toThrow();
+    expect(() => standardDeviation([7])).toThrow();
+})
+
+test("Throw type error - not an array", () => {
+    expect(() => standardDeviation(2)).toThrow();
+    expect(() => standardDeviation("not an array")).toThrow();
+})
+
+test("Throw type error - not a number inside array", () => {
+    expect(() => standardDeviation([5,"not a number",2])).toThrow();
+    expect(() => standardDeviation([1,[2],3])).toThrow();
+})
\ No newline at end of file