Get resource id from resource name in modx revolution

$resource = $modx->getObject('modResource',Resource_Id);

$longTitle = $resource->get('pagetitle');

Here, from above code you can get pagetitle from resource id(Resource_Id).

Get resource id from resource name

$resource = $modx->getObject('modResource','Resource_Name');
$longTitle = $resource->get('id');

in this code you can get resource id from resource pagetitle('Resource_Name').