<?php
$filename = "largefile.txt";
/* get content of $filename in $content */
$content = strtolower(file_get_contents($filename));
/* split $content into array of substrings of $content i.e wordwise */
$wordArray = preg_split('/[^a-z]/', $content, -1, PREG_SPLIT_NO_EMPTY);
/* "stop words", filter them */
$filteredArray = array_filter($wordArray, function($x){
return !preg_match("/^(.|a|an|and|the|this|at|in|or|of|is|for|to)$/",$x);
});
/* get associative array of values from $filteredArray as keys and their frequency count as value */
$wordFrequencyArray = array_count_values($filteredArray);
/* Sort array from higher to lower, keeping keys */
arsort($wordFrequencyArray);
/* grab Top 10, huh sorted? */
$top10words = array_slice($wordFrequencyArray,0,10);
/* display them */
foreach ($top10words as $topWord => $frequency)
echo "$topWord -- $frequency<br/>";
?>