How to check a partial similarity of two strings in PHP

Question

Is it any function in PHP that check the % of similarity of two strings?

For example i have:

$string1=\"Hello how are you doing\" 
$string2= \" hi,          


        

Answer 1

As it's a nice question, I put some effort into it:

<?php
$string1="Hello how are you doing";
$string2= " hi, how are you";

echo 'Compare result: ' . compareStrings($string1, $string2) . '%';
//60%


function compareStrings($s1, $s2) {
    //one is empty, so no result
    if (strlen($s1)==0 || strlen($s2)==0) {
        return 0;
    }

    //replace none alphanumeric charactors
    //i left - in case its used to combine words
    $s1clean = preg_replace("/[^A-Za-z0-9-]/", ' ', $s1);
    $s2clean = preg_replace("/[^A-Za-z0-9-]/", ' ', $s2);

    //remove double spaces
    while (strpos($s1clean, "  ")!==false) {
        $s1clean = str_replace("  ", " ", $s1clean);
    }
    while (strpos($s2clean, "  ")!==false) {
        $s2clean = str_replace("  ", " ", $s2clean);
    }

    //create arrays
    $ar1 = explode(" ",$s1clean);
    $ar2 = explode(" ",$s2clean);
    $l1 = count($ar1);
    $l2 = count($ar2);

    //flip the arrays if needed so ar1 is always largest.
    if ($l2>$l1) {
        $t = $ar2;
        $ar2 = $ar1;
        $ar1 = $t;
    }

    //flip array 2, to make the words the keys
    $ar2 = array_flip($ar2);


    $maxwords = max($l1, $l2);
    $matches = 0;

    //find matching words
    foreach($ar1 as $word) {
        if (array_key_exists($word, $ar2))
            $matches++;
    }

    return ($matches / $maxwords) * 100;    
}
?>

Answer 2

You can use the PHP function similar_text.

int similar_text ( string $first , string $second)

Check the PHP doc at: http://php.net/manual/en/function.similar-text.php

Answer 3

In addition to Alex Siri's answer and according to the following article:

http://docstore.mik.ua/orelly/webprog/php/ch04_06.htm

PHP provides several functions that let you test whether two strings are approximately equal:

$string1="Hello how are you doing" ;
$string2= " hi, how are you";

SOUNDEX

if (soundex($string1) == soundex($string2)) {

  echo "similar";

} else {

  echo "not similar";

}

METAPHONE

if (metaphone($string1) == metaphone($string2)) {

   echo "similar";

} else {

  echo "not similar";

}

SIMILAR TEXT

$similarity = similar_text($string1, $string2);

LEVENSHTEIN

$distance = levenshtein($string1, $string2); 

Answer 4

Ok here is my function that makes it much interesting.

I'm checking approximately similarity of strings.

Here is a criteria I use for that.

1. The order of the words is important
2. The words can have 85% of similarity.

Example:

$string1 = "How much will it cost to me" (string in vocabulary)
$string2 = "How much does costs it "   //("costs" instead "cost" -is a mistake) (user input);

Algorithm: 1) Check the similarity of words and create clean strings with "right" words (in the order it appear in vocabulary). OUTPUT: "how much it cost" 2) create clean string with "right words" in order it appear in user input. OUTPUT: "how much cost it" 3)Compare two outputs - if not the same - return no, else if same return yes.

error_reporting(E_ALL);
ini_set('display_errors', true);

$string1="сколько это стоит ваще" ;
$string2= "сколько будет стоить это будет мне";

if(compareStrings($string1, $string2)) {
 echo "yes";    
} else {
    echo 'no';
}
//echo compareStrings($string1, $string2);

function compareStrings($s1, $s2) {

    if (strlen($s1)==0 || strlen($s2)==0) {
        return 0;
    }

    while (strpos($s1, "  ")!==false) {
        $s1 = str_replace("  ", " ", $s1);
    }
    while (strpos($s2, "  ")!==false) {
        $s2 = str_replace("  ", " ", $s2);
    }

    $ar1 = explode(" ",$s1);
    $ar2 = explode(" ",$s2);
  //  $array1 = array_flip($ar1);
  //  $array2 = array_flip($ar2);
    $l1 = count($ar1);
    $l2 = count($ar2);

 $meaning="";
    $rightorder="";
    $compare=0;
    for ($i=0;$i<$l1;$i++) {


        for ($j=0;$j<$l2;$j++) {

            $compare = (similar_text($ar1[$i],$ar2[$j],$percent)) ;
          //  echo $compare;
if ($percent>=85) {
    $meaning=$meaning." ".$ar1[$i];
    $rightorder=$rightorder." ".$ar1[$j];
    $compare=0;
}

        }


    }
    //print_r($rightorder);
if ($rightorder==$meaning) {
    return true;
} else {
    return false;
}

}

i would love to hear your opinion and suggestion how to improve it

Answer 5

As other answers have already said, you can use similar_text. Here's the demonstration:

$string1="Hello how are you doing" ;
$string2= " hi, how are you";

echo similar_text($string1, $string2, $perc); //12

echo $perc; //61.538461538462

will return 12, and will set in $perc the percentage of similarity as you asked for.