Sorting nested arrays via an Element in each Sub Array

The callback function for usort will receive two of your array entries (which are arrays in themselves) and must answer whether $a comes before or after $b.

For example the function would receive

  $a = array('Lat' => 45, 'Name' => 'Mickey Mouse', ...)
  $b = array('Lat' => 47, ...)

So if you want to sort by Lat element, you would use,

  function sort_by_lat($a, $b)
  {
      return $a['Lat'] - $b['Lat']; // or b - a to sort the other way
  }

  usort($array, "sort_by_lat");

A problem you might have is that this way, if you sorted by longitude, you might consider -1 to be less than +1, and -179 to be less than +180. Which might or might not be what you expect. In this case you would need to use if(), and/or introduce some conversion.

To sort by name, you can do

 if ($a['field'] > $b['field']) return 1;
 if ($a['field'] == $b['field']) return 0;
 return -1;

(again invert +1 and -1 to get sorted the other way).

Don't forget all your data is coming in as strings, so you need to convert the number values to floats to do a proper comparison.

http://codepad.org/p2EMfTDR

$data = array('0'=> array('name' => 'Dr. Smith', 'address' => '3002 Fake Ave.', 'lat' => '20.711158', 'lng' => '10.803578', 'phone' => '714.939.1324'), '1' => array('name' => 'Dr. Paul', 'address' => '801 Fake St.', 'lat' => '10.749917', 'lng' => '20.834388'));

function cmpLat($a, $b)
{
    if(floatval($a['lat']) > floatval($b['lat'])) {
        return 1;
    } elseif(floatval($a['lat']) < floatval($b['lat'])) {
        return -1;
    } else {
        return 0;
    }
}

function cmpLng($a, $b)
{
    if(floatval($a['lng']) > floatval($b['lng'])) {
        return 1;
    } elseif(floatval($a['lng']) < floatval($b['lng'])) {
        return -1;
    } else {
        return 0;
    }
}

usort($data, "cmpLat");

print_r($data);

usort($data, "cmpLng");

print_r($data);