PHP: sort array by half-hour intervals

Question

I have a very specific problem here. I have a multi-dimensional array that I want to sort first by half-hour time intervals, second by dates. The function array_multisort will not meet my requirements.

Example: I want:

array(array("time"=>"12:15",
            "date"=>"2009-03-24"),
      array("time"=>"12:10",
            "date"=>"2009-03-23"),
      array("time"=>"12:00",
            "date"=>"2009-03-24"),
      array("time"=>"11:30",
            "date"=>"2009-03-24"));

To end up as:

array(array("time"=>"11:30",
            "date"=>"2009-03-24"),
      array("time"=>"12:10",
            "date"=>"2009-03-23"),
      array("time"=>"12:00",
            "date"=>"2009-03-24"),
      array("time"=>"12:15",
            "date"=>"2009-03-24"));

I've tried to accomplish this with uksort in combination with my own sorting callback function. This is the code I am currently using:

uksort($myArray, "sortThirties");

function sortThirties($a, $b)
{
    //Get the two times as timestamps relative to today
    $one = strtotime($a['time']);
    $two = strtotime($b['time']);

    //Round them down to the nearest half-hour time
    $one = $one - ($one % 1800);
    $two = $two - ($two % 1800);

    //Return the difference if times are unequal
    //If times are equal, return the difference between dates.
    return ($one == $two ? strcmp($a['date'],$b['date']) : $one - $two);
}

Immediately after running this function, I print out the array with print_r(), and the order of the data appears to be random. What am I missing?

EDIT: It turns out, the order is completely random. I added this line to the sortThirties function:

echo "<BR>",$a['time']," ",$b['time'];

and all I got was 50 pages of <BR>'s.

I know the array is correctly structured because this code executed on the very same array gives me the unsorted data:

foreach($myArray AS $a)
{
    echo "<BR>",$a['date']," ",$a['time'];
}

The only thing I can think of is there must be a problem with uksort. Any thoughts?

Answer 1

Very odd. I just tried your code on an array similar to the one you provided, and it worked great. Possibilities:

• extra whitespace on any of the array times/dates?
• PHP version differences? I noticed that the return value of strtotime() was changed in PHP version 5.1.0

Answer 2

The uksort function sorts the array by keys while usort sorts the array by value and your array to be sorted is acctualy:

$to_sort = array( 
                  0 => array("time"=>"12:15", "date"=>"2009-03-24"),
                  1 => array("time"=>"12:10", "date"=>"2009-03-23"),
                  2 => array("time"=>"12:00", "date"=>"2009-03-24"),
                  3 => array("time"=>"11:30", "date"=>"2009-03-24")
                );

Do you see the difference? :)