src/Baum/SetValidator.php
protected function groupRootsByScope($roots) {
    $rootsGroupedByScope = array();

    foreach($roots as $root) {
      $key = $this->keyForScope($root);

      if ( !isset($rootsGroupedByScope[$key]) )
        $rootsGroupedByScope[$key] = array();

      $rootsGroupedByScope[$key][] = $root;
    }

    return $rootsGroupedByScope;
  }
protected function groupRootsByScope($roots) {
    $rootsGroupedByScope = array();

    foreach($roots as $root) {
      $key = $this->keyForScope($root);

      if ( !isset($rootsGroupedByScope[$key]) )
        $rootsGroupedByScope[$key] = array();

      $rootsGroupedByScope[$key][] = $root;
    }

    return $rootsGroupedByScope;
  }
Given a list of root nodes, it returns an array in which the keys are the
array of the actual scope column values and the values are the root nodes
inside that scope themselves

@param   mixed   $roots
@return  array