Jaro and Jaro-Winkler
distance, measuring similarity between strings on PHP.

Teddy Zugana

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2 min read

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Nov 12, 2023

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<?php

function getCommonCharacters( $string1, $string2, $allowedDistance )
{
 
 $str1_len = strlen($string1);
 $str2_len = strlen($string2);
 $temp_string2 = $string2;
 
  $commonCharacters='';
 
 for($i=0; $i < $str1_len; $i++)
 {
 
   $noMatch = True;
    // compare if char does match inside given allowedDistance
   // and if it does add it to commonCharacters
   for( $j= max( 0, $i-$allowedDistance ); $noMatch && $j < min( $i + $allowedDistance + 1, $str2_len ); $j++)
   {
    if($temp_string2[$j] == $string1[$i])
    {
    $noMatch = False;
    $commonCharacters .= $string1[$i];
    //$temp_string2[$j] = "";
    }
   } 
 }
 
 return $commonCharacters;
}
 
 
function Jaro( $string1, $string2 )
{
 
  $str1_len = strlen( $string1 );
  $str2_len = strlen( $string2 );
  
  // theoretical distance
  $distance = (int) floor(min( $str1_len, $str2_len ) / 2.0); 
  
  // get common characters
  $commons1 = getCommonCharacters( $string1, $string2, $distance );
  $commons2 = getCommonCharacters( $string2, $string1, $distance );
  
  if( ($commons1_len = strlen( $commons1 )) == 0) return 0;
  if( ($commons2_len = strlen( $commons2 )) == 0) return 0;
 // calculate transpositions
  $transpositions = 0;
  $upperBound = min( $commons1_len, $commons2_len );
  
  for( $i = 0; $i < $upperBound; $i++)
  {
  if( $commons1[$i] != $commons2[$i] ) $transpositions++;
  }
  
 $SimiliarityDistacne=@levenshtein($string1, $string1);
  
    //echo $SimiliarityDistacne;
 
 $THREEDATA = 3; 
 if($SimiliarityDistacne == 0)
 {
  $THREEDATA = 3;
 }
 else if($SimiliarityDistacne < 6 && $SimiliarityDistacne > 5)
 {
  $THREEDATA = 3;
 }
 else if ($SimiliarityDistacne < 5)
 {
  $THREEDATA = 6;
 }
  
  $transpositions /= 2.0;
  // return the Jaro distance
  return ($commons1_len/($str1_len) + $commons2_len/($str2_len) + ($commons1_len - $transpositions)/($commons1_len)) / $THREEDATA;
  
}
 
function getPrefixLength( $string1, $string2, $MINPREFIXLENGTH = 4 )
{
 
  $n = min( array( $MINPREFIXLENGTH, strlen($string1), strlen($string2) ) );
  
  for($i = 0; $i < $n; $i++)
  {
   if( $string1[$i] != $string2[$i] )
   {
    // return index of first occurrence of different characters 
    return $i;
   }
  }
  // first n characters are the same 
 
 return $n;
}
 
function JaroWinklerCalculate($string1, $string2, $PREFIXSCALE = 0.1 )
{
 
 $JaroDistance = Jaro( $string1, $string2 );
 
 $prefixLength = getPrefixLength( $string1, $string2 );
 
 return $JaroDistance + $prefixLength * $PREFIXSCALE * (1.0 - $JaroDistance);
}



echo JaroWinkler("Computer Science Portal", "Computer Portal", $PREFIXSCALE = 0.1 );


?>