Changes Requested has been changed as per the sugegstion

modules/index.js

@@ -201,7 +201,7 @@ export { default } from './underscore-array-methods.js';
 
 //Statistical Function
 export { default as sum } from './sum.js';
-export { default as mean } from './avg.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';

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

@@ -1,28 +1,39 @@
-import isArrayLike from './_isArrayLike.js';
-import values from './values.js';
-import cb from './_cb.js';
-import each from './each.js';
-import clone from './clone.js'
-import isNumber from './isNumber.js'
+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).
-export default function median(obj, iteratee, context) {
-    if (!iteratee && _.isEmpty(obj)){
-        return 0;
-    }
-  var tmpObj = [];
-  if (iteratee == null || typeof iteratee == 'number' && typeof obj[0] != 'object' && obj != null) {
-    obj = isArrayLike(obj) ? obj : values(obj);
-    tmpObj = clone(obj);
-    tmpObj.sort(function(f,s){return f-s;});
-  } else {
-    iteratee = cb(iteratee, context);
-    each(obj, function(v, index, list) {
-      computed = iteratee(v, index, list);
-      tmpObj.push(iteratee ? computed : v);
-      tmpObj.sort();
-    });
+// 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 tmpObj.length%2 ? tmpObj[Math.floor(tmpObj.length/2)] : (isNumber(tmpObj[tmpObj.length/2-1]) && isNumber(tmpObj[tmpObj.length/2])) ? (tmpObj[tmpObj.length/2-1]+tmpObj[tmpObj.length/2]) /2 : tmpObj[tmpObj.length/2-1];
+  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

@@ -1,35 +1,19 @@
-import isArrayLike from './_isArrayLike.js';
-import values from './values.js';
-import sortBy from './sortBy.js'
+import isEmpty from './isEmpty';
+import groupBy from './groupBy.js';
+import max from './max.js';
+import first from './first.js';
 
-// Return the mode element (or element-based computation).
-export default function mode(obj, iteratee, context) {
-    if (!iteratee && _.isEmpty(obj)){
-        return 0;
-    }
-    var result = 0;
-    if (iteratee == null || typeof iteratee == 'number' && typeof obj[0] != 'object' && obj != null) {
-        obj = isArrayLike(obj) ? obj : values(obj);
-        obj = sortBy(obj);
-    }else{
-        obj = sortBy(tmpObj,iteratee,context);
-    }
-    var bestStreak = 1;
-    var bestElem = obj[0];
-    var currentStreak = 1;
-    var currentElem = obj[0];
-    for (var i = 1; i < obj.length; i++) {
-      if (obj[i-1] !== obj[i]) {
-        if (currentStreak > bestStreak) {
-          bestStreak = currentStreak;
-          bestElem = currentElem;
-        }
-        currentStreak = 0;
-        currentElem = obj[i];
-      }
+// https://en.wikipedia.org/wiki/Mode_(statistics)
+// Mode is the value that appears most number of times in an array;
 
-      currentStreak++;
-    }
-    result = currentStreak > bestStreak ? currentElem : bestElem;
-    return result
-}
+// 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

@@ -1,19 +1,11 @@
-import isArrayLike from './_isArrayLike.js';
-import values from './values.js';
-import variance from './variance.js'
+import variance from './variance.js';
 
-// Return the standardDeviation element (or element-based computation).
-export default function standardDeviation(obj, iteratee, context) {
-    if (!iteratee && _.isEmpty(obj)){
-        return 0;
-    }
-    var result = 0;
-  if (iteratee == null || typeof iteratee == 'number' && typeof obj[0] != 'object' && obj != null) {
-    obj = isArrayLike(obj) ? obj : values(obj);
-    result = Math.sqrt(variance(obj));
-  } else {
-    result = Math.sqrt(variance(obj,iteratee,context));
-  }
+// https://en.wikipedia.org/wiki/Standard_deviation
 
-  return result;
+// 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

@@ -1,15 +1,12 @@
-import isArrayLike from './_isArrayLike.js';
-import values from './values.js';
-import variance from './variance.js'
-export default function standardError(obj, iteratee, context) {
-    if (!iteratee && _.isEmpty(obj)) return 0;
-    var result = 0;
-    if (iteratee == null || typeof iteratee == 'number' && typeof obj[0] != 'object' && obj != null) {
-        obj = isArrayLike(obj) ? obj : values(obj);
-        result = Math.sqrt(variance(obj)/(obj.length-1));
-    }
-    else{
-        result = Math.sqrt(variance(obj,iterator,context)/(obj.length-1));
-    }
-    return result;
-}
+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

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

modules/sum.js

@@ -1,24 +1,20 @@
 import isArrayLike from './_isArrayLike.js';
 import values from './values.js';
 import cb from './_cb.js';
-import each from './each.js';
+import find from './find.js';
 
 // Return the sum of elements (or element-based computation).
-export default function sum(obj, iteratee, context) {
-    if (!iteratee && _.isEmpty(obj)){
-        return 0;
-    }
+export default function sum(collection, iteratee, context) {
   var result = 0;
-  if (iteratee == null || typeof iteratee == 'number' && typeof obj[0] != 'object' && obj != null) {
-    obj = isArrayLike(obj) ? obj : values(obj);
-    for (var i = 0, length = obj.length; i < length; i++) {
-      result += obj[i];
+  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);
-    each(obj, function(v, index, list) {
-      computed = iteratee(v, index, list);
-      result += computed;
+    find(collection, function(v, index, list) {
+      result += iteratee(v, index, list);;
     });
   }
   return result;

modules/variance.js

@@ -1,34 +1,27 @@
-import isArrayLike from './_isArrayLike.js';
-import values from './values.js';
 import cb from './_cb.js';
-import each from './each.js';
-import mean from './avg.js'
+import mean from './mean.js';
 
-// Return the variance element (or element-based computation).
-export default function variance(obj, iteratee, context) {
-  if (!iteratee && _.isEmpty(obj)){
-      return 0;
-  }
-  var result = 0;
-  if (iteratee == null || typeof iteratee == 'number' && typeof obj[0] != 'object' && obj != null) {
-    obj = isArrayLike(obj) ? obj : values(obj);
-    var avg = mean(obj);
-    var squareDiffs = obj.map(function(value){
-        return (value - avg) * (value - avg);;
-    });
-    result = mean(squareDiffs);
-  } else {
-    var tmpObj;
-    iteratee = cb(iteratee, context);
-    each(obj, function(v, index, list) {
-      computed = iteratee(v, index, list);
-      tmpObj.push(iteratee ? computed : v);
-    });
-    var avg = mean(tmpObj);
-    var squareDiffs = tmpObj.map(function(value){
-        return (value - avg) * (value - avg);;
-    });
-    result = mean(squareDiffs);
-  }
-  return result;
+// 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 +1,4 @@
+(function() {
+    var _ = typeof require == 'function' ? require('..') : window._;
+    QUnit.module('Statistics');
+});