Least Squares Method

LSM.php

<?php
/**
 * Created by PhpStorm.
 * User: kayladnls
 * Date: 12/19/14
 * Time: 4:52 PM
 */

class LeastSquares
{
    private $y_int;
    private $slope;

    /*
     * A method to train the function. Pass in an array of points
     * representing the data that you will be estimating against.
     * ex: $data = [ 0 => [1, 2], 1 => [2, 4]]
     */
    public function train(array $data)
    {
        list($x, $y) = $this->splitInput($data);

        $mean_x = $this->mean($x);
        $mean_y = $this->mean($y);
        $mean_intercept = [$mean_x, $mean_y];

        $barx = array_map(function($x) use($mean_x) {
                return $x - $mean_x;
            }, $x);

        $bary = array_map(function($y) use($mean_y) {
                return $y - $mean_y;
            }, $y);

        $this->slope = $this->calcSlope($barx, $bary);

        $this->y_int = $this->calcYInt($this->slope, $mean_intercept);
    }


    public function estimate($x)
    {
        return $this->y_int + ($this->slope * $x);
    }

    private function calcYInt($slope, $mean_intercept)
    {
        return $mean_intercept[1] - ($slope * $mean_intercept[0]);
    }

    private function splitInput(array $data)
    {
        $x = [];
        $y = [];
        foreach ($data as $datum)
        {
            $x[] = $datum[0];
            $y[] = $datum[1];
        }

        return [$x, $y];
    }

    private function calcSlope($barx, $bary)
    {
        $barxsq = $this->squareArr($barx);

        $barx_times_bary = $this->multArrs($barx, $bary);

        return array_sum($barx_times_bary) / array_sum($barxsq);
    }

    private function multArrs($array1, $arry2)
    {
        return  array_map(function($x, $y) {
                return $x*$y;
            }, $array1, $arry2);
    }

    private function squareArr(array $vals)
    {
        return array_map(
            function ($val)
            {
                return $val*$val;
            },
            $vals
        );
    }

    private function mean(array $vals)
    {
        return array_sum($vals) / count($vals);
    }
}