First, read up on how to get the View/Display pair that contain PHP Array display. This section assumes that you already have the view_name and display_id to be executed. We assume the following variables.
$view_name = the view name
$display_id = the display id
// we assume that the view specified by $view_name has $display_id as its display.
To get the view specified by $view_name
$view = views_get_view($view_name);
To set the display
$view->set_display($display_id);
Optional: to set the arguments
$view->set_arguments('arg1/arg2/arg3');
To set which page to be fetched (if pager is enabled)
$view->set_current_page(1);
To execute it (recommended)
$php_array = $view->preview();
$php_array will contain the view output in the following format:
group1
--item1
----field1
----field2
--item2
----field1
----field2
group2
--item3
----field1
----field2
--item4
----field1
----field2