| 1 | import sumNthPowerDeviations from "./sum_nth_power_deviations";
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| 2 |
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| 3 | /**
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| 4 | * The [variance](http://en.wikipedia.org/wiki/Variance)
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| 5 | * is the sum of squared deviations from the mean.
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| 6 | *
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| 7 | * This is an implementation of variance, not sample variance:
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| 8 | * see the `sampleVariance` method if you want a sample measure.
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| 9 | *
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| 10 | * @param {Array<number>} x a population of one or more data points
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| 11 | * @returns {number} variance: a value greater than or equal to zero.
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| 12 | * zero indicates that all values are identical.
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| 13 | * @throws {Error} if x's length is 0
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| 14 | * @example
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| 15 | * variance([1, 2, 3, 4, 5, 6]); // => 2.9166666666666665
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| 16 | */
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| 17 | function variance(x) {
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| 18 | if (x.length === 0) {
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| 19 | throw new Error("variance requires at least one data point");
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| 20 | }
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| 21 |
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| 22 | // Find the mean of squared deviations between the
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| 23 | // mean value and each value.
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| 24 | return sumNthPowerDeviations(x, 2) / x.length;
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| 25 | }
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| 26 |
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| 27 | export default variance;
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