Simple PHP function to convert Roman numbers to Arabic numbers

romanToArabic.php

<?php

/**
 * ROMAN TO ARABIC NUMBERS
 * @author Axel @mabox.eu
 * @param string $input
 * @return int
 */

function romanToArabic(String $input):int {
    $matrix = [
        'M'	=> 1000,
        'D'	=> 500,
        'C'	=> 100,
        'L'	=> 50,
        'X'	=> 10,
        'V' 	=> 5,
        'I'	=> 1
    ];

    $values = [];

    // First we explode the string as array
    $input = str_split($input);
    // Then we set the corresponding values
    foreach ($input as $i) {
        if (empty($matrix[$i])) {
            throw new Exception('This is NOT a valid roman string');
        }
        array_push($values, $matrix[$i]);
    }

    // Finally running function to detect the sign
    $pos = 0;
    array_walk($values, function(&$val, $key, &$pos) use($values) {
        $pos ++;
        // Looping through the input, starting at next position
        for ($j = $pos; $j < count($values); $j ++) {
            // If the current value is lower than any following value, then we have to substract
            if ($val < $values[$j]) {
                $val = -$val;
                break;
            }
            // Else nothing happens, this remains positive
        }
    }, $pos);
    return array_sum($values);
}

// Give it a try
echo romanToArabic('MMMCDLXIV');