php - Symfony select by defaut various options -

i'm working in form symfony , in select want have, default, options selected.

i've try:

->add('idgroupe',        choicetype::class,        array('label' => 'groupes',              'attr' => array('expanded'=> false,                              'data'=>$g,                              'multiple'=>'true',                              'class' => 'form-control'                             ),              'choices'  => $groupes             )       ) 

where $g array like:

array(1) { [0]=> string(18) "vue1",[1]=> string(18) "vue2" } 

but i've got error:

an exception has been thrown during rendering of template ("notice: array string conversion")

try with:

->add('idgroupe',        choicetype::class,        array('label' => 'groupes',              'attr' => array('class' => 'form-control'                             ),              'expanded'=> false,              'data'=>$g,              'multiple'=>true,              'choices'  => $groupes             )       );