Count word occurrences in a text file, the scalable way (suitable for HUGE files)

WordChart.php

<?php

/**
 *  Counts words in a text files and outputs a chart of the most used.
 */

// Test code, run from CLI
// php WordChart.php freakingLongNovel.txt

$filename = $argv[1];
$o = new WordChart($filename);
$o->toString();

// End example code

class WordChart {

	private $fp = null;
	private $stats = array();
	private $total = 0;

	function WordChart($filename){
		$this->fp = fopen($filename, "r");
		if($this->fp == null){
			throw new Exception("cannot open specified file: $filename", 1);
		} 
		$this->scan();
	}


	private function scan(){
		while (!feof($this->fp)){

			// Fetch a word from stream
			$word="";
			do {
				$char = fread($this->fp, 1);
				if($this->isSeparator($char)){
					break;	
				}
				$word.=$char;
			}
			while(!feof($this->fp) && !$this->isSeparator($char));

			// Clean word from punctuation an extra spaces	
			$word=preg_replace( '/[\-\_[:punct:]0-9\t\r\n\/]/', '', $word);
			$word = strtolower($word);
			
			if($word == ""){
				continue;
			}

			// Update the chart
			$this->total++;
			if(array_key_exists($word, $this->stats)){
				$val = $this->stats[$word];
				if(is_int($val) && $val >= 0){
					$this->stats[$word] += 1;
					continue;
				}
				$this->stats[$word] = 1;
			}
			else {
				$this->stats[$word] = 1;	
			}
		}

		fclose($this->fp);
		arsort($this->stats);	
	}


	public function toString(){
		$i=1; 
		foreach ($this->stats as $word => $score) {
			echo "$i)\t$word\t\t\t($score)\n";
			$i++;
			if($i>40) {
				break;
			}
		}
		echo "total words: $this->total\n";
	}

	private function isSeparator($char){
		return (is_null($char) || $char == ' '  || $char == PHP_EOL);
	}
}