Sort multidimensional array by multiple keys

Question

I'm trying to sort a multidimensional array by multiple keys, and I have no idea where to start. I looked at uasort, but wasn't quite sure how to write a function for what I need.

I need to sort by the state, then event_type, then date.

My array looks like this:

    Array
(
    [0] => Array
        (
            [ID] => 1
            [title] => Boring Meeting
            [date_start] => 2010-07-30
            [time_start] => 06:45:PM
            [time_end] => 
            [state] => new-york
            [event_type] => meeting
        )

    [1] => Array
        (
            [ID] => 2
            [title] => Find My Stapler
            [date_start] => 2010-07-22
            [time_start] => 10:45:AM
            [time_end] => 
            [state] => new-york
            [event_type] => meeting
        )

    [2] => Array
        (
            [ID] => 3
            [title] => Mario Party
            [date_start] => 2010-07-22
            [time_start] => 02:30:PM
            [time_end] => 07:15:PM
            [state] => new-york
            [event_type] => party
        )

    [3] => Array
        (
            [ID] => 4
            [title] => Duct Tape Party
            [date_start] => 2010-07-28
            [time_start] => 01:00:PM
            [time_end] => 
            [state] => california
            [event_type] => party
        )
...... etc

Answer 1

You need array_multisort

$mylist = array(
    array('ID' => 1, 'title' => 'Boring Meeting', 'event_type' => 'meeting'),
    array('ID' => 2, 'title' => 'Find My Stapler', 'event_type' => 'meeting'),
    array('ID' => 3, 'title' => 'Mario Party', 'event_type' => 'party'),
    array('ID' => 4, 'title' => 'Duct Tape Party', 'event_type' => 'party')
);

# get a list of sort columns and their data to pass to array_multisort
$sort = array();
foreach($mylist as $k=>$v) {
    $sort['title'][$k] = $v['title'];
    $sort['event_type'][$k] = $v['event_type'];
}
# sort by event_type desc and then title asc
array_multisort($sort['event_type'], SORT_DESC, $sort['title'], SORT_ASC,$mylist);

As of PHP 5.5.0:

array_multisort(array_column($mylist, 'event_type'), SORT_DESC,
                array_column($mylist, 'title'),      SORT_ASC,
                $mylist);

$mylist is now:

array (
  0 => 
  array (
    'ID' => 4,
    'title' => 'Duct Tape Party',
    'event_type' => 'party',
  ),
  1 => 
  array (
    'ID' => 3,
    'title' => 'Mario Party',
    'event_type' => 'party',
  ),
  2 => 
  array (
    'ID' => 1,
    'title' => 'Boring Meeting',
    'event_type' => 'meeting',
  ),
  3 => 
  array (
    'ID' => 2,
    'title' => 'Find My Stapler',
    'event_type' => 'meeting',
  ),
)