JQuery :: Populate Items Into A Select Using Ajax / Json And Php?

I have a select field. I must fill with options taken from a mysql table.Here is some little php code I have done using codeigniter framework

$idcateg = trim($this->input->post('idcategory'));
$array1 = array(
'result' => $idcateg
);
echo json_encode($array1);

Now, the jQuery call...

$.post("<?=base_url()?>index.php/rubro/list_ajax/", {
'idcategory' : idc },
function(data){

[code]....

The code works fine. When I call the post, I get the categoryid as a result.Now, I should modify the code above, so I can do:post the ajax call sending the category id. this is done get subcategories for this category, and build the array * json_encode the array and echo * get results back in jQuery ajax call, decode and build the < select > field *The array should be built with each element having a sub-array with id and name, right?