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