RegExp PHP show the smallest match - php

Question

I am trying to get the smallest match of a regexp in php.
For example: If I have the words television and telephone and the user input is tel, my regexp should return the smallest word, in this case telephone.
For short I am trying to do like a search script. But for the letters missing in the user input I use this t[a-zA-Z0-9]{0,2}l[a-zA-Z0-9]{0,} so my last letter form the word will followed by N characters.
My question is: How can I do my REGEXP To show the smallest word.

Answer 1

Unfortunately you can't do it. Regex can match what you want, but it doesn't provide any functions to compare submatches. You have to match your whole string, and compare submatches by PHP code in your case.
// your array of matched words
$words = array(...);
$foundWordLength = null;
$foundWord = '';
foreach ($words as $word) {
if (strlen($word) < $foundWordLength || $foundWordLength === null) {
$wordLength = strlen($word);
$foundWord = $word;
}
}
echo $foundWord;

Answer 2

The only way I think you can achieve it using Regular Expressions, is to sort words in desirable order first, in your case from the shortest to the longest.
Then if you have a relatively small amount of words, for the sake of performance, words can be concatenated and checked for the first match simultaneously. It's possible because PHP RegExp implementation performs the search from left to right. See function search_short() in example below.
Anyway, the loop and checking for the word starting from the lowest will work as well. Check function search_long() in example below.
<?php
$given = [
'telephone',
'television',
];
// NB: Do not forget to sanitize user input, i.e. $query
echo (search_short($given, 'tele') ?: 'Nothing found') . PHP_EOL;
echo (search_long($given, 'tele') ?: 'Nothing found') . PHP_EOL;
echo (search_short($given, 't[a-zA-Z0-9]{0,2}l[a-zA-Z0-9]{0,}') ?: 'Nothing found') . PHP_EOL;
echo (search_long($given, 't[a-zA-Z0-9]{0,2}l[a-zA-Z0-9]{0,}') ?: 'Nothing found') . PHP_EOL;
/**
* #param string[] $given
* #param string $query
*
* #return null|string
*/
function search_short($given, $query)
{
// precalculating the length of each word, removing duplicates, sorting
$given = array_map(function ($word) {
return mb_strlen($word); // `mb_strlen()` is O(N) function, while `strlen()` is O(1)
}, array_combine($given, $given));
asort($given);
// preparing the index string
$index = implode(PHP_EOL, array_keys($given));
// and, finally, searching (the multiline flag is set)
preg_match(
sprintf('/^(?<word>%s\w*)$/mu', $query), // injecting the query word
$index,
$matches
);
// the final pattern looks like: "/^(?P<word>tele\w*)$/mui"
if (array_key_exists('word', $matches)) {
return $matches['word'];
}
return null;
}
/**
* #param string[] $given
* #param string $query
*
* #return null|string
*/
function search_long($given, $query)
{
$pattern = sprintf('/^(?<word>%s\w*)$/u', $query);
// precalculating the length of each word, removing duplicates, sorting
$given = array_map(function ($word) {
return mb_strlen($word);
}, array_combine($given, $given));
asort($given);
foreach ($given as $word => $count) {
if (preg_match($pattern, $word, $matches)) {
if (array_key_exists('word', $matches)) {
return $matches['word'];
}
}
}
return false;
}
Of course it's not the most efficient algorithm and might be improved in multiple ways. But for accomplishing this more information about the scope and usage needed.

Answer 3

A Regular Expression engine normally neither does have an intended memory to store complex conditions nor benefits from a programming language features to provide complex comparisons.
You can do your job with a few more lines if tagging php wasn't done aimlessly.
$str = 'television and telephone';
preg_match_all('/tel\w*/', $str, $matches);
usort($matches[0], function($a, $b) {
return strlen($a) <=> strlen($b);
});
echo $matches[0][0];