PHP String levenshtein() Function

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The PHP String levenshtein() function is a built-in method. It is used to calculate the Levenshtein distance among two strings. The Levenshtein distance among two strings is defined as the least number of characters needed to insert, remove, or replace in a given string $string1 to convert it into a string $string2.

The levenshtein() method is not case sensitive. And it is faster than the similar_text() function. However, similar_text() produces a more accurate result with fewer adjustments required.

Syntax

Below is the syntax of the PHP String levenshtein() function −

int levenshtein ( $string1, $string2, $insert, $replace, $delete )

Parameters

Here are the parameters of the levenshtein() function −

• $string1 − (Required) It is one of the strings being evaluated for Levenshtein distance.

• $string2 − (Required) It is second strings being evaluated for Levenshtein distance.

• $insert − (Optional) It is the cost of inserting a character. Default value is 1

• $replace − (Optional) It is the cost of replacing a character. Default value is 1.

• $delete − (Optional) It is the cost of deleting a character. Default value is 1.

Return Value

The levenshtein() function returns the Levenshtein distance between the two given strings, or -1 if one of the strings has more than 255 characters.

PHP Version

First introduced in core PHP 4.0.1, the levenshtein() function continues to function easily in PHP 5, PHP 7, and PHP 8.

Example 1

Here we will the PHP String levenshtein() function and calculate the Levenshtein distance between two strings by applying the default insertion, replacement, and deletion charges.

<?php
   $string1 = "hello";
   $string2 = "hallo";

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

   echo "The Levenshtein distance between '$string1' and '$string2' is: $distance";
?>

Output

Here is the outcome of the following code −

The Levenshtein distance between 'hello' and 'hallo' is: 1

Example 2

In the below PHP code we are using the levenshtein() function and find the Levenshtein distance with custom costs.

<?php
   $string1 = "kitten";
   $string2 = "sitting";

   $distance = levenshtein($string1, $string2, 1, 2, 3);

   echo "The Levenshtein distance between '$string1' and '$string2' (custom costs) is: $distance";
?> 

Output

The above code compares the terms "kitten" and "sitting" to custom prices of 1 for insertion, 2 for replacement, and 3 for removal −

The Levenshtein distance between 'kitten' and 'sitting' (custom costs) is: 5

Example 3

The below program shows how the levenshtein() function is not case-sensitive by comparing two strings with different cases.

<?php
   $string1 = "Tree";
   $string2 = "tree";

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

   echo "The Levenshtein distance between '$string1' and '$string2' (case-insensitive) is: $distance";
?> 

Output

This will create the below output −

The Levenshtein distance between 'Tree' and 'tree' (case-insensitive) is: 0

Example 4

This code example checks how the levenshtein() function handles strings longer than 255 characters.

<?php
   $string1 = str_repeat("a", 256);
   $string2 = "a";

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

   if ($distance == -1) {
      echo "One of the strings exceeds the 255-character limit.";
   } else {
      echo "The Levenshtein distance is: $distance";
   }
?> 

Output

Following is the output of the above code −

The Levenshtein distance is: 255