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feat(mean): combineMeans, a method for combining calculated means
* Adding combineMeans * Avoiding repetition * Fixing unit test formulation
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'use strict'; | ||
/* @flow */ | ||
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/** | ||
* When combining two lists of values for which one already knows the means, | ||
* one does not have to necessary recompute the mean of the combined lists in | ||
* linear time. They can instead use this function to compute the combined | ||
* mean by providing the mean & number of values of the first list and the mean | ||
* & number of values of the second list. | ||
* | ||
* @param {number} mean1 mean of the first list | ||
* @param {number} n1 number of items in the first list | ||
* @param {number} mean2 mean of the second list | ||
* @param {number} n2 number of items in the second list | ||
* @returns {number} the combined mean | ||
* | ||
* @example | ||
* combineMeans(5, 3, 4, 3); // => 4.5 | ||
*/ | ||
function combineMeans(mean1 /*: number*/, n1/*: number */, mean2 /*: number*/, n2/*: number */)/*: number */ { | ||
return (mean1 * n1 + mean2 * n2) / (n1 + n2); | ||
} | ||
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module.exports = combineMeans; |
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/* eslint no-shadow: 0 */ | ||
'use strict'; | ||
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var test = require('tap').test; | ||
var ss = require('../'); | ||
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test('combineMeans', function(t) { | ||
t.test('can combine the means of two lists', function(t) { | ||
var values1 = [8, 3, 4]; | ||
var values2 = [2, 6, 4]; | ||
t.equal(ss.combineMeans(ss.mean(values1), values1.length, ss.mean(values2), values2.length), 4.5); | ||
t.equal(ss.combineMeans(ss.mean(values1), values1.length, ss.mean(values2), values2.length), ss.mean(values1.concat(values2))); | ||
t.end(); | ||
}); | ||
t.end(); | ||
}); |