Weighted merging of multiple Markov Chains

Suppose you have ten text sources, and you generate a new block of text trained from each, and you want to give each its own weighting. You have to weave multiple markov chains together. Here is a class that does just that.

class MultiMarkov {
    private $files;
    private $chains = array();
    private $weights = array();
    private $total_weight = 0;
    public function __construct($init) {
        $total_weight = 0;
        foreach($init as $label => $file_settings) {
            $file = $file_settings['file'];
            $weight = $file_settings['weight'];
            if (!is_integer($weight) || $weight <= 0) {
                throw new Exception (
                    "Weight $weight is not a positive integer.");
            }
            $total_weight += $weight;
            $this->weights[$label] = $weight;
            $words = get_all_words_in_file($file);
            $chain = new Chain($words);
            $this->chains[$label] = $chain;
        }
        $this->total_weight = $total_weight;
    }
    public function setWeights($weights) {
        foreach($weights as $label => $weight) {
            $this->weights[$label] = $weight;
        }
    }
    public function getWeightedRandomChain() {
        $rand = rand(0, $this->total_weight);
        $running_total = 0;
        foreach($this->weights as $label => $weight) {
            $running_total += $weight;
            if ($running_total > $rand) {
                break;
            }
        }
        // echo "$labeln";
        return $this->chains[$label];
    }
    public function getRandomWord() {
        $from_chain = $this->getWeightedRandomChain();
        return $from_chain->getRandomWord();
    }
    public function getChainOfLength($in_word, $length) {

        while (!isset($word) || $word == false) {
            $from_chain = $this->getWeightedRandomChain();
            $word = $from_chain->getNextWord($in_word);

        } 
        if ($length > 1) {
            return $word . $this->getChainOfLength($word, $length - 1);
        } else {
            return $word;
        }
    }
}

To use this class you could do something like so:

<?php 

include 'markov.php';
include 'multi-markov.php';

$files = array(
    'joyce' => array(
        'file' => 'text/joyce.txt',
        'weight' => 10
    ),
    'weitz' => array(
        'file' => 'text/weitz.txt',
        'weight' => 20
    ),
    'sontag' => array(
        'file' => 'text/sontag.txt',
        'weight' => 15
    ),
    'berger' => array(
        'file' => 'text/berger.txt',
        'weight' => 10
    ),
    'tolstoy' => array(
        'file' => 'text/tolstoy.txt',
        'weight' => 19
    ),

);

$builder = new MultiMarkov($files);
$starting_word = $builder->getRandomWord();

$newSentence = $builder->getChainOfLength($starting_word, 160);
echo wordwrap($newSentence, 70, "n");

This text is trained from a variety of great writers writing about aesthetics and the nature of art. Here’s a sample of the output:

praise worthy on the conditions under which has drawn it seemed to me that of reassembling what we would call these conditions ù a novel, painting, to its subject, remains the concept shows, has hardly broken into the standard of all other world, have painted the result of color that “This is often experienced as to himself; so, thanks to fate or love to see in the faculty of a common properties of the world that supreme quality of true painting or theory again. Of course,”Art is very perception of art. Whatis central as a fading coal. The destiny of the word has experienced, and everything else… For myself, I am speaking now that basket from everything else. Each claims that are made by accident when he experiences the oar or that its claim to be answered yes or even seem to be maintained is definable as works of application of movements, lines, colors, shapes, volumes – and sufficient conditions.