PHP实现机器学习之朴素贝叶斯算法详解

$classifier = new Classifier();
$classifier->learn('Symfony is the best', Type::POSITIVE);
$classifier->learn('PhpStorm is great', Type::POSITIVE);
$classifier->learn('Iltar complains a lot', Type::NEGATIVE);
$classifier->learn('No Symfony is bad', Type::NEGATIVE);
var_dump($classifier->guess('Symfony is great')); // string(8) "positive"
var_dump($classifier->guess('I complain a lot')); // string(8) "negative"

<?php
class Type
{
 const POSITIVE = 'positive';
 const NEGATIVE = 'negative';
}
class Classifier
{
 private $types = [Type::POSITIVE, Type::NEGATIVE];
 private $words = [Type::POSITIVE => [], Type::NEGATIVE => []];
 private $documents = [Type::POSITIVE => 0, Type::NEGATIVE => 0];
 public function guess($statement)
 {
 $words  = $this->getWords($statement); // get the words
 $best_likelihood = 0;
 $best_type = null;
 foreach ($this->types as $type) {
  $likelihood = $this->pTotal($type); // calculate P(Type)
  foreach ($words as $word) {
  $likelihood *= $this->p($word, $type); // calculate P(word, Type)
  }
  if ($likelihood > $best_likelihood) {
  $best_likelihood = $likelihood;
  $best_type = $type;
  }
 }
 return $best_type;
 }
 public function learn($statement, $type)
 {
 $words = $this->getWords($statement);
 foreach ($words as $word) {
  if (!isset($this->words[$type][$word])) {
  $this->words[$type][$word] = 0;
  }
  $this->words[$type][$word]++; // increment the word count for the type
 }
 $this->documents[$type]++; // increment the document count for the type
 }
 public function p($word, $type)
 {
 $count = 0;
 if (isset($this->words[$type][$word])) {
  $count = $this->words[$type][$word];
 }
 return ($count + 1) / (array_sum($this->words[$type]) + 1);
 }
 public function pTotal($type)
 {
 return ($this->documents[$type] + 1) / (array_sum($this->documents) + 1);
 }
 public function getWords($string)
 {
 return preg_split('/\s+/', preg_replace('/[^A-Za-z0-9\s]/', '', strtolower($string)));
 }
}
$classifier = new Classifier();
$classifier->learn('Symfony is the best', Type::POSITIVE);
$classifier->learn('PhpStorm is great', Type::POSITIVE);
$classifier->learn('Iltar complains a lot', Type::NEGATIVE);
$classifier->learn('No Symfony is bad', Type::NEGATIVE);
var_dump($classifier->guess('Symfony is great')); // string(8) "positive"
var_dump($classifier->guess('I complain a lot')); // string(8) "negative"