mergeByFunction, mergeByProperty

merge_by.php

<?php

  /**
   * Merge two arrays by extracting a key for each element with a function $f
   * @param $f function which returns a scalar given any of the members of $array1 or $array2
   * @param $array1
   * @param ...
   *
   * @return array keyed by the output of $f on elements of the arrays passed in
   */
  public static function mergeByFunction ($f, $array1) {
    $merged = array();

    $arguments = func_get_args();
    if (count($arguments) < 2) {
      throw new InvalidArgumentException(__METHOD__." cannot apply function to empty arguments");
    }
    $f = array_shift($arguments);
    if (!is_callable($f)) {
      throw new InvalidArgumentException(__METHOD__." needs a valid function!");
    }

    foreach ($arguments as $array_argument) {
      if (!is_array($array_argument)) {
        $array_argument = array($array_argument);
      }
      foreach ($array_argument as $array_member) {
        if ($array_member) {
          $merged[$f($array_member)] = $array_member;
        }
      }
    }

    return $merged;
  }

  /**
   * A convenience function for mergeByFunction that covers a very general 
   * case where you want to merge two or more arrays of objects by a common 
   * property of those objects. Later objects with the same property value 
   * will replace earlier ones.
   *
   * @param $property string of the common property of the objects 
   * @param $array1 array of objects of the same type
   * @param ... more arrays of objects of the same type
   *
   * @return array of all the objects keyed by the value of the individual properties
   */
  public static function mergeByProperty ($property, $array1) {
    $merged = array();

    $arguments = func_get_args();
    if (count($arguments) < 2) {
      throw new InvalidArgumentException(__METHOD__." cannot extract property from empty arguments");
    }
    $property = array_shift($arguments);

    $extract_function = create_function('$object', 'return $object->'.$property.';');
    // for the curious, this can also be expressed as:
    /*
    $extract_function = function ($object) use ($property) {
      return $object->$property;
    };
   */

    array_unshift($arguments, $extract_function);

    $merged = call_user_func_array(array(__CLASS__, "mergeByFunction"), $arguments);

    return $merged;
  }