How to build a 2d array with static and dynamic data while looping?

I'm using a foreach loop to create an array from database values like so:

foreach ($query->result_array() as $row) {
   array(
      'user_id'  => $user_id,
      'post_id'  => $row['id'],
      'time'     => '0',
      'platform' => $platform
   );
}

Let's say I pull 2 rows, I need to make this foreach create a multidimensional array in the following format:

$data = array(
    array(
       'user_id'  => '12', 
       'post_id'  => '37822', 
       'time'     => '0',
       'platform' => 'email'
    ),
    array(
       'user_id'  => '12', 
       'post_id'  => '48319', 
       'time'     => '0',
       'platform' => 'email'
    ),
);

You can first declare an empty array :

$results = array();

then, each time you have a new row, add it to that array :

$results[] = $row;

Or, anyway, to add anything into that array :

$results[] = array( something here );

In your specific case, you'd probably use something like this :

$results = array();
foreach ($query->result_array() as $row) {
    $results[] = array(
                    'user_id' => $user_id, 
                    'post_id' => $row['id'], 
                    'time' => '0', 
                    'platform' => $platform
                );
}

As a reference, the corresponding section of the PHP manual : Creating/modifying with square bracket syntax.