Roman numerals to numbers in string

Question

I have this string:

$string = 'Hello IV WorldX';

And I want to replace all roman numerals to integers.

I have the following function to convert roman to integer:

function roman2number($roman){
    $conv = array(
        array("letter" => 'I', "number" => 1),
        array("letter" => 'V', "number" => 5),
        array("letter" => 'X', "number" => 10),
        array("letter" => 'L', "number" => 50),
        array("letter" => 'C', "number" => 100),
        array("letter" => 'D', "number" => 500),
        array("letter" => 'M', "number" => 1000),
        array("letter" => 0, "number" => 0)
    );
    $arabic = 0;
    $state = 0;
    $sidx = 0;
    $len = strlen($roman);

    while ($len >= 0) {
        $i = 0;
        $sidx = $len;
        while ($conv[$i]['number'] > 0) {
            if (strtoupper(@$roman[$sidx]) == $conv[$i]['letter']) {
                if ($state > $conv[$i]['number']) {
                    $arabic -= $conv[$i]['number'];
                } else {
                    $arabic += $conv[$i]['number'];
                    $state = $conv[$i]['number'];
                }
            }
            $i++;
        }
        $len--;
    }
    return($arabic);
}

echo roman2number('IV');

Works great (try it on ideone). How do I search & replace through the string to replace all instances of roman numerals. Something like:

$string = romans_to_numbers_in_string($string);

Sounds like regex needs to come to the rescue... or?

Answer 1

Here's a simple regex to match roman numerals:

\b[0IVXLCDM]+\b

So, you can implement romans_to_numbers_in_string like this:

function romans_to_numbers_in_string($string) {
    return preg_replace_callback('/\b[0IVXLCDM]+\b/', function($m) {
           return roman2number($m[0]);
           },$string);
}

There are some problems with this regex. Like, if you have a string like this:

I like roman numerals

It will become:

1 like roman numerals

Depending on your requirements, you can let it be, or you can modify the regex so that it doesn't convert single I's to numbers.