PHP levenshtein() Function

The levenshtein() function returns the Levenshtein distance between two strings.The Levenshtein distance is the number of characters you have to replace, insert or delete to transform string1 into string2.

By default, PHP gives each operation (replace, insert, and delete) equal weight. However, you can define the cost of each operation by setting the optional insert, replace, and delete parameters.

int levenshtein ( string $str1 , string $str2 )

int levenshtein ( string $str1 , string $str2 , int $cost_ins , int $cost_rep , int $cost_del )

The Levenshtein distance is defined as the minimal number of characters you have to replace, insert or delete to transform str1 into str2. The complexity of the algorithm is O(m*n), where n and m are the length of str1 and str2 (rather good when compared to similar_text(), which is O(max(n,m)**3), but still expensive).

In its simplest form the function will take only the two strings as parameter and will calculate just the number of insert, replace and delete operations needed to transform str1 into str2. A second variant will take three additional parameters that define the cost of insert, replace and delete operations. This is more general and adaptive than variant one, but not as efficient.

Example -

<?php
// input misspelled word
$input = 'carrrot';

// array of words to check against
$words  = array('apple','pineapple','banana','orange',
                'radish','carrot','pea','bean','potato');

// no shortest distance found, yet
$shortest = -1;

// loop through words to find the closest
foreach ($words as $word) {

// calculate the distance between the input word,
    // and the current word
    $lev = levenshtein($input, $word);

// check for an exact match
    if ($lev == 0) {

// closest word is this one (exact match)
        $closest = $word;
        $shortest = 0;

// break out of the loop; we've found an exact match
        break;
    }

// if this distance is less than the next found shortest
    // distance, OR if a next shortest word has not yet been found
    if ($lev <= $shortest || $shortest < 0) {
        // set the closest match, and shortest distance
        $closest  = $word;
        $shortest = $lev;
    }
}

echo "Input word: $input\n";
if ($shortest == 0) {
    echo "Exact match found: $closest\n";
} else {
    echo "Did you mean: $closest?\n";
}

Parameter	Description
str1	One of the strings being evaluated for Levenshtein distance.
str2	One of the strings being evaluated for Levenshtein distance.
cost_ins	Defines the cost of insertion.
cost_rep	Defines the cost of replacement.
cost_del	Defines the cost of deletion.

This function returns the Levenshtein-Distance between the two argument strings or -1, if one of the argument strings is longer than the limit of 255 characters.