Innmind / ProvisionerBundle

<?php

namespace Innmind\ProvisionerBundle;

/**

 * Small helper to linearize data points

 */

class Math

{

    /**

     * Determine slope and intercept variables of the affine function

     * that best fit the given datapoints

     *

     * @param array $data Array keys as x axis and values as y axis

     *

     * @return array Like ['slope' => float, 'intercept' => float]

     */

    public static function linearRegression(array $data)

    {

        $count = count($data);

        $x = array_keys($data);

        $y = array_values($data);

        foreach ($x as &$value) {

            $value = (float) $value;

        }

        foreach ($y as &$value) {

            $value = (float) $value;

        }

        $xSum = array_sum($x);

        $ySum = array_sum($y);

        $xxSum = 0;

        $xySum = 0;

        for ($i = 0; $i < $count; $i++) {

            $xySum += $x[$i] * $y[$i];

            $xxSum += $x[$i] * $x[$i];

        }

        $slope = (($count * $xySum) - ($xSum * $ySum)) / (($count * $xxSum) - ($xSum * $xSum));

        $intercept = ($ySum - ($slope * $xSum)) / $count;

        return [

            'slope' => $slope,

            'intercept' => $intercept

        ];

    }

}