Calculate Levenshtein distance between two strings

# levenshtein

(PHP 4 >= 4.0.1, PHP 5, PHP 7, PHP 8)

levenshtein — Calculate Levenshtein distance between two strings

### Description

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

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() - Calculate the soundex key of a string
- similar_text() - Calculate the similarity between two strings
- metaphone() - Calculate the metaphone key of a string

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