jQuery order json list from php? - php

Question

i am sending an ordered json_encode list of some MySQL tables, from php, but when i retrieve it with jquery it is not in order any more? everything works fine and in order on the php side. it's the client side that i'm having trouble with. i think the problem is that i'm sending a multidimensional array from php as json. what would be the most efficient solution? also why has the order changed when retrieved by jQuery.
PHP CODE:
$user_data = array();
while($row = mysql_fetch_array($retval, MYSQL_ASSOC){
$user_id = $row['user_id'];
if(!isset($user_data[$user_id]){
$user_data[$user_id] = array(
'first_name' => $row['first_name'],
'last_name' => $row['last_name'],
'dept' => $row['dept'],
'quals' => array()
);
}
$quals = array(
'qual_cat' => $row['qual_cat'],
'qual' => $row['qual'],
'count' => $row['count']
)
$user_data[$user_id]['quals'][] = $quals;
}
echo json_encode($user_data);
jQuery:
$.post('page.php', function(post){
$.each(post, function(i,data){
alert(data.first_name+' '+data.last_name+' - '+data.dept);
});
});
PHP VAR_DUMP:
array
10 =>
array
'first_name' => string 'David' (length=5)
'last_name' => string 'Dan' (length=3)
'dept' => string 'web' (length=3)
'count' => string '5' (length=1)
'quals' =>
array
0 =>
array
...
1 =>
array
...
2 =>
array
...
3 =>
array
...
4 =>
array
...

Answer 1

In php, array is by default associative, so that's why you have this behavior as associative array order is not guaranteed (as per explanation in the link given by benedict_w).
To overcome this, you could try the following:
echo json_encode(array_values($user_data));
This will effectively turn your json from
["10":{prop1:val1, prop2:val2}, "25":{prop1:val1, prop2:val2}]
into
[{prop1:val1, prop2:val2}, {prop1:val1, prop2:val2}]
If you need to keep track of the id, put it inside your user_data in your php:
if(!isset($user_data[$user_id]){
$user_data[$user_id] = array(
'id' => $user_id,
'first_name' => $row['first_name'],
'last_name' => $row['last_name'],
'dept' => $row['dept'],
'quals' => array()
);
}