- array_slice: documentation ( source)
- preg_match_all: documentation ( source)
- array_unique: documentation ( source)
- join: documentation ( source)
<?php
$string = 'Samsung UN32EH4003 32-inch 720p 60Hz LED HDTV (Black)';
echo shorten_string($string);
$arr=array();
preg_match_all('/\b([0-9A-Za-z]{3,})\b/', $string, $arr);
$keywords = array_slice(array_unique($arr[0]),0,3);
echo join('<br/>', $keywords);