- array_values: documentation ( source)
- array_keys: documentation ( source)
- json_encode: documentation ( source)
<?php
$index_norm = array("key1" => "foobar", "key2" => "bananaramam", "key3" => "spam");
$result = array(
"ids"=>array_keys($index_norm),
"weights"=>array_values($index_norm)
);
echo json_encode($result);