Algorithms for string similarities (better than Levenshtein, and similar_text)? Php, Js

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Here’s a solution that I’ve come up to. It’s based on Tim’s suggestion of comparing the order of subsequent charachters. Some results:

  • jonas / jonax : 0.8
  • jonas / sjona : 0.68
  • jonas / sjonas : 0.66
  • jonas / asjon : 0.52
  • jonas / xxjon : 0.36

I’m sure i isn’t perfect, and that it could be optimized, but nevertheless it seems to produce the results that I’m after…
One weak spot is that when strings have different length, it produces different result when the values are swapped… 

static public function string_compare($str_a, $str_b) 
{
    $length = strlen($str_a);
    $length_b = strlen($str_b);

    $i = 0;
    $segmentcount = 0;
    $segmentsinfo = array();
    $segment="";
    while ($i < $length) 
    {
        $char = substr($str_a, $i, 1);
        if (strpos($str_b, $char) !== FALSE) 
        {               
            $segment = $segment.$char;
            if (strpos($str_b, $segment) !== FALSE) 
            {
                $segmentpos_a = $i - strlen($segment) + 1;
                $segmentpos_b = strpos($str_b, $segment);
                $positiondiff = abs($segmentpos_a - $segmentpos_b);
                $posfactor = ($length - $positiondiff) / $length_b; // <-- ?
                $lengthfactor = strlen($segment)/$length;
                $segmentsinfo[$segmentcount] = array( 'segment' => $segment, 'score' => ($posfactor * $lengthfactor));
            } 
            else 
            {
                $segment="";
                $i--;
                $segmentcount++;
            } 
        } 
        else 
        {
            $segment="";
            $segmentcount++;
        }
        $i++;
    }   

    // PHP 5.3 lambda in array_map      
    $totalscore = array_sum(array_map(function($v) { return $v['score'];  }, $segmentsinfo));
    return $totalscore;     
}

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