function spam_bayesian_filter in Spam 5

Simple Bayesian logic to determine the probability that the passed in array of tokens is spam.

Parameters

$tokens An array of tokens.:

Return value

An integer from 1 to 99 which is the probability that the array of tokens passed to this function are spam.

1 call to spam_bayesian_filter()

spam_content_filter in ./spam.module

Determine whether or not provided text is spam.

File

./spam.module, line 1181

Code

function spam_bayesian_filter($tokens = array()) {

  /* Lookup each token in the databse to assign a probability that the token
   * is spam.  If the token doesn't exist in the database, assign a default
   * probability.  Finally, calculate how far this probability is away from
   * a median of 50%.
   */
  foreach ($tokens as $token) {

    // TODO:  Optimize, this is a lot of database queries!
    $p = db_fetch_object(db_query("SELECT probability FROM {spam_tokens} WHERE token = '%s'", $token));
    if (!$p->probability) {
      $p->probability = variable_get('spam_default_probability', 40);
    }
    $t["{$token},{$p->probability}"] = abs($p->probability - 50);
  }

  /* Sort token array so those tokens with the largest "drift" come first.
   * Drift is this distance from a median of 50%.
   */
  asort($t);

  /* Take the n most "interesting" tokens from the top of the token array.
   * The larger a token's drift, the more interesting it is.
   */
  $keys = array_keys($t);
  $max = variable_get('spam_interesting_tokens', 15);
  $total = 0;
  for ($i = 0; $i < $max; $i++) {
    if ($pair = array_pop($keys)) {
      $p = explode(',', $pair);
      $total = $total + $p[1];
      spam_log(SPAM_DEBUG, t("bayesian filter: token '@token' spam probability @percent%", array(
        '@token' => $p[0],
        '@percent' => $p[1],
      )));
    }
    else {

      // we've looked at all the tokens
      break;
    }
  }
  $probability = round($total / $i, 1);
  spam_log(SPAM_LOG, t("bayesian filter: examined @num tokens, spam probability of @percent%", array(
    '@num' => $i,
    '@percent' => $probability,
  )));
  return $probability;
}