Illuminate\Database\Query\Builder::groupBy PHP Method

    public function groupBy(...$groups)
    {
        foreach ($groups as $group) {
            $this->groups = array_merge((array) $this->groups, is_array($group) ? $group : [$group]);
        }
        return $this;
    }

 public function execute(Builder $query)
 {
     foreach ($this->getValuesIterator() as $groupBy) {
         $query->groupBy($groupBy->getValue());
     }
     return $query;
 }