Statistical Functions

modules/index.js

@@ -198,3 +198,13 @@ export { default as chunk } from './chunk.js';
 // `underscore.js` and `index-default.js`.
 export { default as mixin } from './mixin.js';
 export { default } from './underscore-array-methods.js';
+
+//Statistical Function
+export { default as sum } from './sum.js';
+export { default as mean } from './mean.js';
+export { default as median } from './median.js';
+export { default as standardDeviation } from './standardDeviation.js';
+export { default as variance } from './variance.js';
+export { default as mode } from './mode.js';
+export { default as standardError } from './standardError.js';
+export { default as statRange } from './statRange.js';

modules/mean.js

@@ -0,0 +1,11 @@
+import size from './size.js';
+import sum from './sum.js';
+
+// Return the average/mean element (or element-based computation).
+export default function mean(collection, iteratee, context) {
+  var length = size(collection);
+
+  if (length < 1) return 0;
+
+  return sum(collection, iteratee, context) / length;
+}

modules/median.js

@@ -0,0 +1,39 @@
+import map from './map.js'
+import isNumber from './isNumber.js';
+import isEmpty from './isEmpty';
+
+// https://en.wikipedia.org/wiki/Median
+// Return the median element (or element-based computation).
+// First arrays is sorted in ascending order
+// Then middle element is the median in the given array
+// Calulation of median is done using the following method;
+
+/* Odd elements
+   If the array has odd numbers then value is the middle element
+   example: [1,2,3,4,5,6,7]
+   length: 7
+   middle value: (length+1)/2 = 4
+   median : array[4] = 4
+*/
+
+/* Even elements
+   If the array has odd numbers then value is the middle element
+   example: [1,5,5,8,10,12,13,15]
+   length: 8
+   middle value: ((length/2) + ((length/2)+1))/2  = 
+   median : (8+10)/2 = 9
+*/
+export default function median(collection, iteratee, context) {
+  if (isEmpty(collection)) return undefined;
+
+  if (typeof iteratee == 'number' && collection != null && typeof collection[0] != 'object') {
+    iteratee = null;
+  }
+  var tmpArr = map(obj, iteratee, context).sort();
+
+  return tmpArr.length%2 ?
+             tmpArr[Math.floor(tmpArr.length/2)] : 
+            (isNumber(tmpArr[tmpArr.length/2-1]) && isNumber(tmpArr[tmpArr.length/2])) ?
+                 (tmpArr[tmpArr.length/2-1]+tmpArr[tmpArr.length/2]) /2 : 
+                 tmpArr[tmpArr.length/2-1];
+}

modules/mode.js

@@ -0,0 +1,19 @@
+import isEmpty from './isEmpty';
+import groupBy from './groupBy.js';
+import max from './max.js';
+import first from './first.js';
+
+// https://en.wikipedia.org/wiki/Mode_(statistics)
+// Mode is the value that appears most number of times in an array;
+
+// Array is sorted and traversed to find the most frequent element in the array
+// Return the mode element (or element-based computation).
+export default function mode(collection, iteratee, context) {
+  if (isEmpty(collection)) return;
+
+  if (typeof iteratee == 'number' && collection != null && typeof collection[0] != 'object') {
+    iteratee = null;
+  }
+  var groups = groupBy(collection, iteratee, context);
+  return first(max(groups, 'length'));
+}

modules/standardDeviation.js

@@ -0,0 +1,11 @@
+import variance from './variance.js';
+
+// https://en.wikipedia.org/wiki/Standard_deviation
+
+// Suare root of the variance value
+// Variance is calulation can go through the variance function for description (https://en.wikipedia.org/wiki/Variance)
+// Return the standardDeviation based on element-based computation.
+
+export default function standardDeviation(collection, iteratee, context) {
+  return Math.sqrt(variance(collection, iteratee, context));
+}

modules/standardError.js

@@ -0,0 +1,12 @@
+import variance from './variance.js';
+import size from './size.js';
+
+//https://en.wikipedia.org/wiki/Standard_error
+
+// Square root of variance divided by the number of elements (length -1)
+// Variance is calulation can go through the variance function for description (https://en.wikipedia.org/wiki/Variance)
+
+// Return the standardError based on element-based computation.
+export default function standardError(collection, iteratee, context) {
+    return Math.sqrt(variance(collection, iteratee, context)/(size(collection) - 1));
+}

modules/statRange.js

@@ -0,0 +1,6 @@
+import max from './max.js';
+import min from './min.js';
+
+export default function statRange(collection,iteratee,context){
+    return max(collection,iteratee,context) - min(collection,iteratee,context);
+}

modules/sum.js

@@ -0,0 +1,21 @@
+import isArrayLike from './_isArrayLike.js';
+import values from './values.js';
+import cb from './_cb.js';
+import find from './find.js';
+
+// Return the sum of elements (or element-based computation).
+export default function sum(collection, iteratee, context) {
+  var result = 0;
+  if (iteratee == null || typeof iteratee == 'number'  && collection != null && typeof collection[0] != 'object') {
+    collection = isArrayLike(collection) ? collection : values(collection);
+    for (var i = 0, length = collection.length; i < length; i++) {
+      result += collection[i];
+    }
+  } else {
+    iteratee = cb(iteratee, context);
+    find(collection, function(v, index, list) {
+      result += iteratee(v, index, list);;
+    });
+  }
+  return result;
+}

modules/variance.js

@@ -0,0 +1,27 @@
+import cb from './_cb.js';
+import mean from './mean.js';
+
+// https://en.wikipedia.org/wiki/Variance
+
+// Steps to calculate variance
+// 1. Average value of the array
+// 2. New array is calulated by negating the value with the average value and to the power of 2.
+// 3. Average value of the new array is the variance
+
+// Return the variance based on the computation.
+export default function variance(collection, iteratee, context) {
+  if (typeof iteratee == 'number' && collection != null && typeof collection[0] != 'object') iteratee = null;
+
+  iteratee = cb(iteratee, context);
+
+  var computed = [];
+  var avg = mean(collection, function(value, key, collection) {
+    var result = iteratee(value, key, collection);
+    computed.push(result);
+    return result;
+  });
+  return mean(computed, function(value) {
+    var difference = value - avg;
+    return difference * difference;
+  });
+}

test/statistics.js

@@ -0,0 +1,13 @@
+(function() {
+    var _ = typeof require == 'function' ? require('..') : window._;
+    QUnit.module('Statistics');
+    QUnit.test('mean', function(assert) {
+
+        assert.strictEqual(_.mean(null), 0, 'can handle null/undefined');
+        assert.strictEqual(_.mean(void 0), -Infinity, 'can handle null/undefined');
+        assert.strictEqual(_.mean([1, 2, 3]),2,"Avearge of the numbers in the collection");
+
+        assert.strictEqual(_.mean({}), 0, 'Avearge value of an empty object');
+        assert.strictEqual(_.mean([]), 0, 'Avearge value of an empty array');
+    });
+});