public function unique_units()
    {
        $unique_units = [];
        foreach ($this->units as $u) {
            $unique_units[(string)$u] = $u;
        }
        return $unique_units;
    }
public function unique_units()
    {
        $unique_units = [];
        foreach ($this->units as $u) {
            $unique_units[(string)$u] = $u;
        }
        return $unique_units;
    }
public function unique_units ( ) { $ unique_units = [ ] ; foreach ( $ this -> units as $ u ) { $ unique_units [ ( string ) $ u ] = $ u ; } return $ unique_units ; }
Get the unique units.

@return array
Get the unique units .