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similar_text

(PHP 4, PHP 5, PHP 7, PHP 8)

similar_text — 二つの文字列の間の類似性を計算する

説明

similar_text(string $string1, string $string2, float &$percent = null): int

この関数は、Programming Classics: Implementing the World's Best Algorithms by Oliver (ISBN 0-131-00413-1) に記述されたように二つの文字列の間の類似性を計算します。この実装は Oliver の擬似コードの様にスタックを使用せず、プロセス全体の速度が改善されるかどうかにかかわらず再帰呼び出しを行うことに注意してください。このアルゴリズムの計算量は、O(N**3) であることにも注意してください。ただし、N は最も長い文字列の長さです。

パラメータ

string1: 最初の文字列。
string2: 次の文字列。

注意:
string1 と string2 を入れ替えると、結果は異なるものになります; 例を参照ください。
percent: 3 番目の引数としてリファレンスを渡すことにより、 similar_text() は類似性をパーセントで計算します。これは、similar_text() の結果を、与えられた文字列の長さの平均を 100 倍した値で割ることで出しています。

戻り値

両方の文字列でマッチした文字の数を返します。

マッチする文字数は、最初の共通最長部分文字列を探し、同じことをその文字列の前後の文字列に対して再帰的に行うことで計算されます。そうして見つかった全ての共通部分文字列の長さが追加されます。

例

例1 similar_text() で、引数を入れ替えた場合の例

以下のコードは、 string1 と string2 を入れ替えると、異なる結果になる可能性を示しています。

<?php
$sim = similar_text('bafoobar', 'barfoo', $perc);
echo "類似度: $sim ($perc %)\n";
$sim = similar_text('barfoo', 'bafoobar', $perc);
echo "類似度: $sim ($perc %)\n";

上の例の出力は、たとえば以下のようになります。

類似度: 5 (71.428571428571 %)
類似度: 3 (42.857142857143 %)

参考

levenshtein() - 二つの文字列のレーベンシュタイン距離を計算する
soundex() - 文字列の soundex キーを計算する

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User Contributed Notes 11 notes

down

111

SPAM HATER ¶

12 years ago

Hey there,



Be aware when using this function, that the order of passing the strings is very important if you want to calculate the percentage of similarity, in fact, altering the variables will give a very different result, example :



<?php

$var_1 = 'PHP IS GREAT';

$var_2 = 'WITH MYSQL';



similar_text($var_1, $var_2, $percent);



echo $percent;

// 27.272727272727



similar_text($var_2, $var_1, $percent);



echo $percent;

// 18.181818181818

?>

down

daniel dot karbach at localhorst dot tv ¶

14 years ago

Please note that this function calculates a similarity of 0 (zero) for two empty strings.

<?php
similar_text("", "", $sim);
echo $sim; // "0"
?>

down

I_HATE_SPAMMER- PAZ! ¶

10 years ago

Actually similar_text() is not bad...
it works good. But before processing i think is a good way to make a little mod like this

$var_1 = strtoupper("doggy");
$var_2 = strtoupper("Dog");

similar_text($var_1, $var_2, $percent); 

echo $percent; // output is 75 but without strtoupper output is 50

down

ryan at derokorian dot com ¶

10 years ago

Note that this function is case sensitive:

<?php

$var1 = 'Hello';
$var2 = 'Hello';
$var3 = 'hello';

echo similar_text($var1, $var2);  // 5
echo similar_text($var1, $var3);  // 4

down

vasyl at vasyltech dot com ¶

8 years ago

Recursive algorithm usually is very elegant one. I found a way to get better precision without the recursion. Imagine two different (or same) length ribbons with letters on each. You simply shifting one ribbon to left till it matches the letter the first.

<?php

function similarity($str1, $str2) {
    $len1 = strlen($str1);
    $len2 = strlen($str2);
    
    $max = max($len1, $len2);
    $similarity = $i = $j = 0;
    
    while (($i < $len1) && isset($str2[$j])) {
        if ($str1[$i] == $str2[$j]) {
            $similarity++;
            $i++;
            $j++;
        } elseif ($len1 < $len2) {
            $len1++;
            $j++;
        } elseif ($len1 > $len2) {
            $i++;
            $len1--;
        } else {
            $i++;
            $j++;
        }
    }

    return round($similarity / $max, 2);
}

$str1 = '12345678901234567890';
$str2 = '12345678991234567890';

echo 'Similarity: ' . (similarity($str1, $str2) * 100) . '%';
?>

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daniel at reflexionsdesign dot com ¶

23 years ago

If performance is an issue, you may wish to use the levenshtein() function instead, which has a considerably better complexity of O(str1 * str2).

down

julius at infoguiden dot no ¶

21 years ago

If you have reserved names in a database that you don't want others to use, i find this to work pretty good. 

I added strtoupper to the variables to validate typing only. Taking case into consideration will decrease similarity. 



<?php

$query = mysql_query("select * from $table") or die("Query failed");



while ($row = mysql_fetch_array($query)) {

      similar_text(strtoupper($_POST['name']), strtoupper($row['reserved']), $similarity_pst);

      if (number_format($similarity_pst, 0) > 90){

        $too_similar = $row['reserved'];

        print "The name you entered is too similar the reserved name &quot;".$row['reserved']."&quot;";

        break;

       }

    }

?>

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Paul ¶

17 years ago

The speed issues for similar_text seem to be only an issue for long sections of text (>20000 chars).

I found a huge performance improvement in my application by just testing if the string to be tested was less than 20000 chars before calling similar_text.

20000+ took 3-5 secs to process, anything else (10000 and below) took a fraction of a second.
Fortunately for me, there was only a handful of instances with >20000 chars which I couldn't get a comparison % for.

down

Anonymous ¶

4 years ago

$result = similar_text ('ab', 'a', $percent);

> $percent: 66.666666666666671

down

georgesk at hotmail dot com ¶

22 years ago

Well, as mentioned above the speed is O(N^3), i've done a longest common subsequence way that is O(m.n) where m and n are the length of str1 and str2, the result is a percentage and it seems to be exactly the same as similar_text percentage but with better performance... here's the 3 functions i'm using..



<?php

function LCS_Length($s1, $s2)

{

  $m = strlen($s1);

  $n = strlen($s2);



  //this table will be used to compute the LCS-Length, only 128 chars per string are considered

  $LCS_Length_Table = array(array(128),array(128)); 

  

  

  //reset the 2 cols in the table

  for($i=1; $i < $m; $i++) $LCS_Length_Table[$i][0]=0;

  for($j=0; $j < $n; $j++) $LCS_Length_Table[0][$j]=0;



  for ($i=1; $i <= $m; $i++) {

    for ($j=1; $j <= $n; $j++) {

      if ($s1[$i-1]==$s2[$j-1])

        $LCS_Length_Table[$i][$j] = $LCS_Length_Table[$i-1][$j-1] + 1;

      else if ($LCS_Length_Table[$i-1][$j] >= $LCS_Length_Table[$i][$j-1])

        $LCS_Length_Table[$i][$j] = $LCS_Length_Table[$i-1][$j];

      else

        $LCS_Length_Table[$i][$j] = $LCS_Length_Table[$i][$j-1];

    }

  }

  return $LCS_Length_Table[$m][$n];

}



function str_lcsfix($s)

{

  $s = str_replace(" ","",$s);

  $s = ereg_replace("[��������]","e", $s);

  $s = ereg_replace("[������������]","a", $s);

  $s = ereg_replace("[��������]","i", $s);

  $s = ereg_replace("[���������]","o", $s);

  $s = ereg_replace("[��������]","u", $s);

  $s = ereg_replace("[�]","c", $s);

  return $s;

}

  

function get_lcs($s1, $s2)

{

  //ok, now replace all spaces with nothing

  $s1 = strtolower(str_lcsfix($s1));

  $s2 = strtolower(str_lcsfix($s2));

  

  $lcs = LCS_Length($s1,$s2); //longest common sub sequence



  $ms = (strlen($s1) + strlen($s2)) / 2;



  return (($lcs*100)/$ms);

}

?>



you can skip calling str_lcsfix if you don't worry about accentuated characters and things like that or you can add up to it or modify it for faster performance, i think ereg is not the fastest way?

hope this helps.

Georges

down

-1

pablo dot pazos at cabolabs dot com ¶

3 years ago

To calculate the percentage of similarity between two strings without depending on the order of the parameters and be case insensitive, I use this function based on levenshtein's distance:

<?php

  // string similarity calculated using levenshtein
  static function similarity($a, $b)
  {
    return 1 - (levenshtein(strtoupper($a), strtoupper($b)) / max(strlen($a), strlen($b)));
  }

?>

This will always return a number between 0 and 1, representing the percentage, for instance 0.8 represents 80% similar strings.

If you want this to be case-sensitive, just remove the strtoupper() functions.

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Atelier ”慶”

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PHPのお勉強！

similar_text

説明

パラメータ

戻り値

例

参考

Found A Problem?

User Contributed Notes 11 notes