String Functions
PHP Manual

levenshtein

Calculate Levenshtein distance between two strings

Description

int levenshtein(
    string $string1,
    string $string2,
    int $insertion_cost = 1,
    int $replacement_cost = 1,
    int $deletion_cost = 1
)

The Levenshtein distance is defined as the minimal number of characters you have to replace, insert or delete to transform string1 into string2. The complexity of the algorithm is O(m*n), where n and m are the length of string1 and string2 (rather good when compared to similar_text, which is O(max(n,m)**3), but still expensive).

If insertion_cost, replacement_cost and/or deletion_cost are unequal to 1, the algorithm adapts to choose the cheapest transforms. E.g. if $insertion_cost + $deletion_cost < $replacement_cost, no replacements will be done, but rather inserts and deletions instead.

Parameters

string1

One of the strings being evaluated for Levenshtein distance.

string2

One of the strings being evaluated for Levenshtein distance.

insertion_cost

Defines the cost of insertion.

replacement_cost

Defines the cost of replacement.

deletion_cost

Defines the cost of deletion.

Return Values

This function returns the Levenshtein-Distance between the two argument strings.

Changelog

Version Description
8.0.0 Prior to this version, levenshtein had to be called with either two or five arguments.
8.0.0 Prior to this version, levenshtein would return -1 if one of the argument strings is longer than 255 characters.

Examples

Example #1 levenshtein 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";
}

?>

The above example will output:

Input word: carrrot
Did you mean: carrot?

See Also

  • soundex
  • similar_text
  • metaphone