102 lines
1.8 KiB
Markdown
102 lines
1.8 KiB
Markdown
---
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id: 5a23c84252665b21eecc7e03
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title: Cumulative standard deviation
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challengeType: 5
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forumTopicId: 302240
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dashedName: cumulative-standard-deviation
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---
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# --description--
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Write a function that takes an array of numbers as parameter and returns the [standard deviation](https://en.wikipedia.org/wiki/Standard Deviation) of the series.
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# --hints--
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`standardDeviation` should be a function.
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```js
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assert(typeof standardDeviation == 'function');
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```
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`standardDeviation([2, 4, 4, 4, 5, 5, 7, 9])` should return a number.
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```js
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assert(typeof standardDeviation([2, 4, 4, 4, 5, 5, 7, 9]) == 'number');
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```
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`standardDeviation([2, 4, 4, 4, 5, 5, 7, 9])` should return `2`.
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```js
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assert.equal(standardDeviation([2, 4, 4, 4, 5, 5, 7, 9]), 2);
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```
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`standardDeviation([600, 470, 170, 430, 300])` should return `147.323`.
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```js
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assert.equal(standardDeviation([600, 470, 170, 430, 300]), 147.323);
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```
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`standardDeviation([75, 83, 96, 100, 121, 125])` should return `18.239`.
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```js
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assert.equal(standardDeviation([75, 83, 96, 100, 121, 125]), 18.239);
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```
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`standardDeviation([23, 37, 45, 49, 56, 63, 63, 70, 72, 82])` should return `16.87`.
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```js
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assert.equal(
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standardDeviation([23, 37, 45, 49, 56, 63, 63, 70, 72, 82]),
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16.87
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);
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```
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`standardDeviation([271, 354, 296, 301, 333, 326, 285, 298, 327, 316, 287, 314])` should return `22.631`.
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```js
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assert.equal(
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standardDeviation([
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271,
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354,
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296,
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301,
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333,
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326,
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285,
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298,
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327,
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316,
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287,
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314
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]),
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22.631
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);
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```
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# --seed--
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## --seed-contents--
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```js
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function standardDeviation(arr) {
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}
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```
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# --solutions--
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```js
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function standardDeviation(arr) {
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var sum = 0,
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sum_sq = 0,
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n = arr.length;
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arr.forEach(function(e) {
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sum += e;
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sum_sq += e * e;
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});
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var std_dev = Math.sqrt(sum_sq / n - Math.pow(sum / n, 2));
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return Math.round(std_dev * 1000) / 1000;
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}
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```
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