Display a group fieldset using form state api.
<?php
/**
* Display group group_name if control field field_control_name has value 2
*/
function ji_custom_field_group_build_pre_render_alter(&$element) {
if(isset($element['group_name'])){
$element['group_name']['#states'] = array(
'visible' => array(
':input[name="field_control_name[und]"]' => array('value' => 2),
),
);
}
}
?>
--
Links:
http://api.drupalhelp.net/api/field_group/field_group.module/function/field_group_build_pre_render/7
http://timonweb.com/programmatically-hiding-a-fieldgroup-on-a-node-display-in-drupal-7