PHP は、ファイルまたは配列内の単語の頻度を計算するメソッドを実装します。

<?php
$str = file_get_contents("/path/to/file.txt"); //get string from file
preg_match_all("/\b(\w+[-]\w+)|(\w+)\b/",$str,$r); //place words into array $r - this includes hyphenated words
$words = array_count_values(array_map("strtolower",$r[0])); //create new array - with case-insensitive count
arsort($words); //order from high to low
print_r($words)

<?php
$filename = "/path/to/file.txt";
$handle = fopen($filename,"r");
if ($handle === false) {
 exit;
}
$word = "";
while (false !== ($letter = fgetc($handle))) {
 if ($letter == &#39; &#39;) {
  $results[$word]++;
  $word = "";
 }
 else {
  $word .= $letter;
 }
}
fclose($handle);
print_r($results);