similar_text

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

similar_textCalcule la similarité de deux chaînes

Description

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

Calcule la similarité entre les deux chaînes string1 et string2, selon la méthode décrite dans Programming Classics: Implementing the World's Best Algorithms by Oliver (ISBN 0-131-00413-1). Notez que cette implémentation n'utilise pas la méthode de pile comme dans le pseudo code d'Oliver, mais des appels récursifs, ce qui accélère ou pas le processus. Notez que la complexité de l'algorithme est en O(N**3) où N est la taille de la plus grande chaîne.

Liste de paramètres

string1

La première chaîne.

string2

La seconde chaîne.

Note:

Inverser string1 et string2 peut produire des résultats différents ; voir l'exemple ci-dessous.

percent

En passant une référence en tant que troisième argument, similar_text() va calculer la similarité en pourcentage, en divisant le résultat de similar_text() par la moyenne de la longueur des chaîne de caractères fournies fois 100.

Valeurs de retour

Retourne le nombre de caractères correspondant dans les deux chaîne de caractères.

Le nombre de caractères correspondant est calculés en trouvant la première plus longue sous-chaîne commune, et puis faire ceci pour les préfixes et les sufixes, de façon récursive. La longueur de toutes les sous-chaînes communes sont ajoutées.

Exemples

Exemple #1 Exemple de similar_text() en inversant les arguments

Cet exemple montre qu'inverser les arguments string1 et string2 peut produire des résultats différents.

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

Résultat de l'exemple ci-dessus est similaire à :

similarity: 5 (71.428571428571 %)
similarity: 3 (42.857142857143 %)

Voir aussi

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User Contributed Notes 11 notes

up
108
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
?>
up
93
daniel dot karbach at localhorst dot tv
13 years ago
Please note that this function calculates a similarity of 0 (zero) for two empty strings.

<?php
similar_text
("", "", $sim);
echo
$sim; // "0"
?>
up
22
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
up
19
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
up
15
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) . '%';
?>
up
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.
up
9
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).
up
11
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.
up
12
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;
       }
    }
?>
up
3
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
up
-1
Anonymous
4 years ago
$result = similar_text ('ab', 'a', $percent);

> $percent: 66.666666666666671
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