Statistical Functions

modules/mean.js

@@ -1,7 +1,7 @@
 import size from './size.js';
 import sum from './sum.js';
 
-// Return the average/mean element (or element-based computation).
+// Compute the average of the numbers obtained from the collection
 export default function mean(collection, iteratee, context) {
   var length = size(collection);
 

modules/median.js

@@ -9,19 +9,11 @@ import isEmpty from './isEmpty';
 // 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
+   If the array has odd numbers then median is the middle element
 */
 
 /* 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
+   If the array has even numbers then average of middle two numbers is the median value
 */
 export default function median(collection, iteratee, context) {
   if (isEmpty(collection)) return undefined;
@@ -31,9 +23,7 @@ export default function median(collection, iteratee, context) {
   }
   var tmpArr = map(collection, 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];
+  return tmpArr.length % 2 ?
+             tmpArr[Math.floor(tmpArr.length / 2)] : 
+                 (tmpArr[tmpArr.length / 2 - 1] + tmpArr[tmpArr.length / 2]) / 2
 }

modules/mode.js

@@ -3,11 +3,9 @@ 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;
+// Return the element (or element-based computation) that appears most frequently in the collection.
 
-// Array is sorted and traversed to find the most frequent element in the array
-// Return the mode element (or element-based computation).
+// https://en.wikipedia.org/wiki/Mode_(statistics)
 export default function mode(collection, iteratee, context) {
   if (isEmpty(collection)) return;
 

modules/standardDeviation.js

@@ -1,11 +1,7 @@
 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.
-
+// https://en.wikipedia.org/wiki/Standard_deviation
 export default function standardDeviation(collection, iteratee, context) {
   return Math.sqrt(variance(collection, iteratee, context));
 }

modules/standardError.js

@@ -1,12 +1,9 @@
 import variance from './variance.js';
 import size from './size.js';
 
-//https://en.wikipedia.org/wiki/Standard_error
+// Return the standard error of the mean based on element-based computation.
 
-// 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.
+// https://en.wikipedia.org/wiki/Standard_error
 export default function standardError(collection, iteratee, context) {
     return Math.sqrt(variance(collection, iteratee, context)/(size(collection) - 1));
 }

modules/statRange.js

@@ -1,6 +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);
+export default function statRange(collection, iteratee, context){
+    return max(collection, iteratee, context) - min(collection, iteratee, context);
 }

modules/variance.js

@@ -1,14 +1,10 @@
 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 of the numeric elements of the collection,
+// optionally after transforming them through `iteratee`.
 
-// Return the variance based on the computation.
+// https://en.wikipedia.org/wiki/Variance
 export default function variance(collection, iteratee, context) {
   if (typeof iteratee == 'number' && collection != null && typeof collection[0] != 'object') iteratee = null;
 

test/statistics.js

@@ -4,7 +4,7 @@
     QUnit.test('mean', function(assert) {
 
         assert.strictEqual(_.mean(null), 0, 'can handle null/undefined');
-        assert.strictEqual(_.mean(void 0), 0, 'can handle null/undefined');
+        assert.strictEqual(_.mean(void 0), 0, 'can handle 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');
@@ -13,7 +13,7 @@
     QUnit.test('median', function(assert) {
 
         assert.strictEqual(_.median(null), undefined, 'can handle null/undefined');
-        assert.strictEqual(_.median(void 0), undefined, 'can handle null/undefined');
+        assert.strictEqual(_.median(void 0), undefined, 'can handle undefined');
         assert.strictEqual(_.median([1, 2, 3]), 2, "Median of the numbers in the collection");
         assert.strictEqual(_.median([1, 2, 3, 4]), 2.5, "Median of the numbers in the collection");
         assert.strictEqual(_.median({}), undefined, 'Median value of an empty object');
@@ -23,7 +23,7 @@
     QUnit.test('sum', function(assert) {
 
         assert.strictEqual(_.sum(null), 0, 'can handle null/undefined');
-        assert.strictEqual(_.sum(void 0), 0, 'can handle null/undefined');
+        assert.strictEqual(_.sum(void 0), 0, 'can handle undefined');
         assert.strictEqual(_.sum([1, 2, 3]), 6, "SUM of the numbers in the collection");
         assert.strictEqual(_.sum([1, 2, 3, 4]), 10, "SUM of the numbers in the collection");
         assert.strictEqual(_.sum({}), 0, 'sum value of an empty object');
@@ -33,7 +33,7 @@
     QUnit.test('variance', function(assert) {
 
         assert.strictEqual(_.variance(null), 0, 'can handle null/undefined');
-        assert.strictEqual(_.variance(void 0), 0, 'can handle null/undefined');
+        assert.strictEqual(_.variance(void 0), 0, 'can handle undefined');
         assert.strictEqual(_.variance([0, 1, 2, 3, 4]), 2, "variance of the numbers in the collection");
         assert.strictEqual(_.variance([1, 2, 3, 4]), 1.25, "variance of the numbers in the collection");
         assert.strictEqual(_.variance({}), 0, 'variance value of an empty object');
@@ -43,7 +43,7 @@
     QUnit.test('standardDeviation', function(assert) {
 
         assert.strictEqual(_.standardDeviation(null), 0, 'can handle null/undefined');
-        assert.strictEqual(_.standardDeviation(void 0), 0, 'can handle null/undefined');
+        assert.strictEqual(_.standardDeviation(void 0), 0, 'can handle undefined');
         assert.strictEqual(_.standardDeviation([0, 1, 2, 3, 4]), 1.4142135623730951, "Standard Deviation of the numbers in the collection");
         assert.strictEqual(_.standardDeviation([1, 2, 3, 4]), 1.118033988749895, "Standard Deviation of the numbers in the collection");
         assert.strictEqual(_.standardDeviation({}), 0, 'Standard Deviation value of an empty object');
@@ -53,7 +53,7 @@
     QUnit.test('standardError', function(assert) {
 
         assert.strictEqual(_.standardError(null), 0, 'can handle null/undefined');
-        assert.strictEqual(_.standardError(void 0), 0, 'can handle null/undefined');
+        assert.strictEqual(_.standardError(void 0), 0, 'can handle undefined');
         assert.strictEqual(_.standardError([0, 1, 2, 3, 4]), 0.7071067811865476, "Standard Error of the numbers in the collection");
         assert.strictEqual(_.standardError([1, 2, 3, 4]), 0.6454972243679028, "Standard Error of the numbers in the collection");
         assert.strictEqual(_.standardError({}), 0, 'Standard Error value of an empty object');
@@ -63,7 +63,7 @@
     QUnit.test('mode', function(assert) {
 
         assert.strictEqual(_.mode(null), undefined, 'can handle null/undefined');
-        assert.strictEqual(_.mode(void 0), undefined, 'can handle null/undefined');
+        assert.strictEqual(_.mode(void 0), undefined, 'can handle undefined');
         assert.strictEqual(_.mode([0, 1, 2, 3, 4]), 0, "Mode of the numbers in the collection");
         assert.strictEqual(_.mode([1, 1, 3, 4]), 1, "Mode of the numbers in the collection");
         assert.strictEqual(_.mode({}), undefined, 'Mode value of an empty object');
@@ -73,7 +73,7 @@
     QUnit.test('statRange', function(assert) {
 
         assert.strictEqual(_.statRange(null), -Infinity, 'can handle null/undefined');
-        assert.strictEqual(_.statRange(void 0), -Infinity, 'can handle null/undefined');
+        assert.strictEqual(_.statRange(void 0), -Infinity, 'can handle undefined');
         assert.strictEqual(_.statRange([0, 1, 2, 3, 4]), 4, "Stat Range of the numbers in the collection");
         assert.strictEqual(_.statRange([1, 1, 3, 4]), 3, "Stat Range of the numbers in the collection");
         assert.strictEqual(_.statRange({}), -Infinity, 'Stat Range value of an empty object');