Statistical Functions

modules/index.js

@@ -198,3 +198,14 @@ 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';
+export { default as percentile } from './percentile.js';

modules/mean.js

@@ -0,0 +1,11 @@
+import size from './size.js';
+import sum from './sum.js';
+
+// Compute the average of the numbers obtained from the collection
+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 +1,19 @@
+import map from './map.js'
+import isEmpty from './isEmpty';
+
+// https://en.wikipedia.org/wiki/Median
+// Calulation of median is done using the following method.
+// If the array has odd numbers then median is the middle element.
+// 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;
+
+  if (typeof iteratee == 'number' && collection != null && typeof collection[0] != 'object') {
+    iteratee = null;
+  }
+  var tmpArr = map(collection, iteratee, context).sort();
+
+  return tmpArr.length % 2 ?
+             tmpArr[Math.floor(tmpArr.length / 2)] : 
+                 (tmpArr[tmpArr.length / 2 - 1] + tmpArr[tmpArr.length / 2]) / 2;
+}

modules/mode.js

@@ -0,0 +1,16 @@
+import isEmpty from './isEmpty';
+import groupBy from './groupBy.js';
+import max from './max.js';
+import first from './first.js';
+
+// Return the element (or element-based computation) that appears most frequently in the collection.
+// https://en.wikipedia.org/wiki/Mode_(statistics)
+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/percentile.js

@@ -0,0 +1,21 @@
+import isEmpty from './isEmpty';
+import sortBy from './sortBy.js';
+
+// Return the percentile value of the numeric elements from the collection
+//Ex : 50th,75th,99th etc.
+//https://en.wikipedia.org/wiki/Percentile
+export default function percentile(collection, percentile) {
+  if (isEmpty(collection)) return 0;
+  if (typeof percentile !== 'number') throw new TypeError('Percentile must be a number between 0 - 100');
+  if (percentile <= 0) return collection[0];
+  if (percentile >= 100) return collection[collection.length - 1];
+
+  collection = sortBy(collection);
+  var index = (percentile / 100) * (collection.length - 1),
+    lowerIndex = Math.floor(index),
+    upperIndex = lowerIndex + 1,
+    weight = index % 1;
+
+  if (upperIndex >= collection.length) return collection[lowerIndex];
+  return collection[lowerIndex] * (1 - weight) + collection[upperIndex] * weight;
+}

modules/standardDeviation.js

@@ -0,0 +1,7 @@
+import variance from './variance.js';
+
+// 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

@@ -0,0 +1,8 @@
+import variance from './variance.js';
+import size from './size.js';
+
+// Return the standard error of the mean 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

@@ -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 +1,24 @@
+import cb from './_cb.js';
+import mean from './mean.js';
+
+// Return the variance of the numeric elements of the collection,
+// optionally after transforming them through `iteratee`.
+// 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;
+  }
+
+  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 +1,86 @@
+(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), 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');
+  });
+
+  QUnit.test('median', function(assert) {
+    assert.strictEqual(_.median(null), 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');
+    assert.strictEqual(_.median([]), undefined, 'Median value of an empty array');
+  });
+
+  QUnit.test('sum', function(assert) {
+    assert.strictEqual(_.sum(null), 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');
+    assert.strictEqual(_.sum([]), 0, 'sum value of an empty array');
+  });
+
+  QUnit.test('variance', function(assert) {
+    assert.strictEqual(_.variance(null), 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');
+    assert.strictEqual(_.variance([]), 0, 'variance value of an empty array');
+  });
+
+  QUnit.test('standardDeviation', function(assert) {
+    assert.strictEqual(_.standardDeviation(null), 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');
+    assert.strictEqual(_.standardDeviation([]), 0, 'Standard Deviation value of an empty array');
+  });
+
+  QUnit.test('standardError', function(assert) {
+    assert.strictEqual(_.standardError(null), 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');
+    assert.strictEqual(_.standardError([]), 0, 'Standard Error value of an empty array');
+  });
+
+  QUnit.test('mode', function(assert) {
+    assert.strictEqual(_.mode(null), 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');
+    assert.strictEqual(_.mode([]), undefined, 'Mode value of an empty array');
+  });
+
+  QUnit.test('statRange', function(assert) {
+    assert.strictEqual(_.statRange(null), -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');
+    assert.strictEqual(_.statRange([]), -Infinity, 'Stat Range value of an empty array');
+  });
+
+  QUnit.test('percentile', function(assert) {
+    assert.strictEqual(_.percentile(null, 25), 0, 'can handle null/undefined');
+    assert.strictEqual(_.percentile(void 0, 50), 0, 'can handle undefined');
+    assert.strictEqual(_.percentile([0, 1, 2, 3, 4], 75), 3, "75th percentile of the numbers in the collection");
+    assert.strictEqual(_.percentile([1, 1, 3, 4], 50), 2, "50th of the numbers in the collection");
+    assert.strictEqual(_.percentile({}, 10), 0, 'Percentile value of an empty object');
+    assert.strictEqual(_.percentile([], 50), 0, 'Percentile value of an empty array');
+    assert.raises(function() {
+      _.percentile([1, 1, 3, 4], "50")
+    }, TypeError, 'Percentile must be a number between 0 - 100');
+ });
+}());