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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<refentry xml:id="function.levenshtein" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
<refnamediv>
<refname>levenshtein</refname>
<refpurpose>Calculate Levenshtein distance between two strings</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<methodsynopsis>
<type>int</type><methodname>levenshtein</methodname>
<methodparam><type>string</type><parameter>string1</parameter></methodparam>
<methodparam><type>string</type><parameter>string2</parameter></methodparam>
<methodparam choice="opt"><type>int</type><parameter>insertion_cost</parameter><initializer>1</initializer></methodparam>
<methodparam choice="opt"><type>int</type><parameter>replacement_cost</parameter><initializer>1</initializer></methodparam>
<methodparam choice="opt"><type>int</type><parameter>deletion_cost</parameter><initializer>1</initializer></methodparam>
</methodsynopsis>
<para>
The Levenshtein distance is defined as the minimal number of
characters you have to replace, insert or delete to transform
<parameter>string1</parameter> into <parameter>string2</parameter>.
The complexity of the algorithm is <literal>O(m*n)</literal>,
where <literal>n</literal> and <literal>m</literal> are the
length of <parameter>string1</parameter> and
<parameter>string2</parameter> (rather good when compared to
<function>similar_text</function>, which is <literal>O(max(n,m)**3)</literal>,
but still expensive).
</para>
<para>
If <parameter>insertion_cost</parameter>, <parameter>replacement_cost</parameter>
and/or <parameter>deletion_cost</parameter> are unequal to <literal>1</literal>,
the algorithm adapts to choose the cheapest transforms.
E.g. if <code>$insertion_cost + $deletion_cost < $replacement_cost</code>,
no replacements will be done, but rather inserts and deletions instead.
</para>
</refsect1>
<refsect1 role="parameters">
&reftitle.parameters;
<para>
<variablelist>
<varlistentry>
<term><parameter>string1</parameter></term>
<listitem>
<para>
One of the strings being evaluated for Levenshtein distance.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>string2</parameter></term>
<listitem>
<para>
One of the strings being evaluated for Levenshtein distance.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>insertion_cost</parameter></term>
<listitem>
<para>
Defines the cost of insertion.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>replacement_cost</parameter></term>
<listitem>
<para>
Defines the cost of replacement.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>deletion_cost</parameter></term>
<listitem>
<para>
Defines the cost of deletion.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect1>
<refsect1 role="returnvalues">
&reftitle.returnvalues;
<para>
This function returns the Levenshtein-Distance between the
two argument strings.
</para>
</refsect1>
<refsect1 role="changelog">
&reftitle.changelog;
<informaltable>
<tgroup cols="2">
<thead>
<row>
<entry>&Version;</entry>
<entry>&Description;</entry>
</row>
</thead>
<tbody>
<row>
<entry>8.0.0</entry>
<entry>
Prior to this version, <function>levenshtein</function> had to be called
with either two or five arguments.
</entry>
</row>
<row>
<entry>8.0.0</entry>
<entry>
Prior to this version, <function>levenshtein</function> would return <literal>-1</literal>
if one of the argument strings is longer than 255 characters.
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</refsect1>
<refsect1 role="examples">
&reftitle.examples;
<para>
<example>
<title><function>levenshtein</function> example</title>
<programlisting role="php">
<![CDATA[
<?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";
}
?>
]]>
</programlisting>
&example.outputs;
<screen>
<![CDATA[
Input word: carrrot
Did you mean: carrot?
]]>
</screen>
</example>
</para>
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<para>
<simplelist>
<member><function>soundex</function></member>
<member><function>similar_text</function></member>
<member><function>metaphone</function></member>
</simplelist>
</para>
</refsect1>
</refentry>
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