Merge branch 'master' of github.com:bda-research/node-ds

Grubbs.js

@@ -4,6 +4,8 @@ module.exports = class Grubbs {
     constructor(data, alpha) {
         if (!(data instanceof Array)) {
             throw new Error('data must be an array');
+        } else if (data.length < 3) {
+            throw new Error('data length must be at least 3');
         }
         this.data = data;
         this.alpha = alpha || 0.05;

README.md

@@ -39,6 +39,8 @@ A common data-structure and basic algorithm implemention in javascript
     * [Merge-Sort](#sorting-algorithms)
     * [Quick-Sort](#sorting-algorithms)
     * [Heap-Sort](#sorting-algorithms)
+  * [Statistics Algorithms](#statistics-algorithms)
+    * [Grubbs](#grubbs)
 * [Test](#test)
 * [Contributing to node-ds](#contributing-to-node-ds)
 
@@ -242,6 +244,19 @@ Random.shuffle(a); // say [6, 9, 3, <b>1, 4, 2, 8</b>, 5, 7]
 SortFamily.insertionSort(a, compare, 3, 6); // outputs [6, 9, 3, <b>8, 4, 2, 1</b>, 5, 7]
 </code></pre>
 
+### Statistics Algorithms
+
+Find out outliers from the given data array based on some basic mathematical calculation(average、stdev).
+
+#### Grubbs
+```javascript
+const Grubbs = require('node-ds/Grubbs.js');
+
+let data = [7, 9, 2, 6, 3, 5, 7, 2, 4, 20];
+let grubbs = new Grubbs(data);
+grubbs.getOutliers();//outputs [9], means the number 20 is outlier
+```
+
 ## Test
 Like most other packages, just run test suite and check code coverage by following commands:
 

tests/Grubbs.js

@@ -4,13 +4,45 @@ const Grubbs = require('../Grubbs');
 let data = null;
 
 describe("Grubbs", function () {
-    beforeEach(() => {
-        data = [7, 9, 2, 6, 3, 5, 7, 2, 4, 20];
+    it('data must be an array', function () {
+        try {
+            new Grubbs(data);
+        } catch (e) {
+            e.should.be.instanceof(Error);
+        }
+    });
+
+    it('data length must be at least 3', function () {
+        data = [1, 100];
+        try {
+            new Grubbs(data);
+        } catch (e) {
+            e.should.be.instanceof(Error);
+        }
+    });
+
+    it('unable to tell outliers when data is distributed in two extremes', function () {
+        data = [1, 1, 100, 100];
+        let grubbs1 = new Grubbs(data);
+        let outliers1 = grubbs1.getOutliers();
+
+        data = [1, 1, 1, 100, 100];
+        let grubbs2 = new Grubbs(data);
+        let outliers2 = grubbs2.getOutliers();
+
+        data = [1, 1, 100, 100, 100];
+        let grubbs3 = new Grubbs(data);
+        let outliers3 = grubbs3.getOutliers();
+
+        should.equal(outliers1.length, 0);
+        should.equal(outliers2.length, 0);
+        should.equal(outliers3.length, 0);
     });
+
     it('20 should be outlier', function () {
+        data = [7, 9, 2, 6, 3, 5, 7, 2, 4, 20];
         let grubbs = new Grubbs(data);
         let outliers = grubbs.getOutliers();
-        console.log(outliers)
         outliers.should.be.instanceof(Array);
         should.equal(outliers.length, 1);
         should.equal(outliers[0], 9);