42 lines
819 B
PHP
42 lines
819 B
PHP
<?php
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declare(strict_types=1);
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namespace Phpml\Math\Statistic;
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use Phpml\Exception\InvalidArgumentException;
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class StandardDeviation
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{
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/**
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* @param array|float[] $a
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*
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* @throws InvalidArgumentException
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*/
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public static function population(array $a, bool $sample = true): float
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{
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if (empty($a)) {
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throw InvalidArgumentException::arrayCantBeEmpty();
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}
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$n = count($a);
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if ($sample && $n === 1) {
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throw InvalidArgumentException::arraySizeToSmall(2);
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}
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$mean = Mean::arithmetic($a);
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$carry = 0.0;
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foreach ($a as $val) {
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$d = $val - $mean;
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$carry += $d * $d;
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}
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if ($sample) {
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--$n;
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}
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return sqrt((float) ($carry / $n));
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}
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}
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