Illuminate\Support\Collection::collapse PHP Method

    public function collapse()
    {
        return new static(Arr::collapse($this->items));
    }

 public function rowsUngrouped()
 {
     if (!isset($this->rows)) {
         $this->rows = $this->rows();
     }
     return $this->rows instanceof GroupedCollection ? new Collection($this->rows->collapse()) : $this->rows;
 }