sort array by value that is calculated from the array

Question

I have the lat and lng from a user from the database in an array and I have my lat and lng

Now I want to calculate the distance and sort the users from my database with

Answer 1

Create a distance function:

function getDistance ($lat, $lon)
{
    global $mylng, $mylat;
    $x1 = deg2rad($mylng);
    $x2 = deg2rad($lon);
    $y1 = deg2rad($mylat);
    $y2 = deg2rad($lat);

    $dist = acos(sin($x1)*sin($x2)+cos($x1)*cos($x2)*cos($y2 - $y1))*(6378.137);
    return $dist;
}

Create a comparison function:

function compareDistance ($user1, $user2)
{
    return getDistance ($user1['lat'], $user1['lng']) - getDistance ($user2['lat'], $user2['lng']);
}

Then you can pass your array through uasort:

uasort ($users, 'compareDistance');

See http://php.net/manual/en/function.uasort.php for more information.

EDIT:

Your program could be rewritten:

function getDistance ($lat, $lon)
{
    global $mylng, $mylat;

    $x1 = deg2rad($mylng);
    $x2 = deg2rad($lon);
    $y1 = deg2rad($mylat);
    $y2 = deg2rad($lat);

    $dist = acos(sin($x1)*sin($x2)+cos($x1)*cos($x2)*cos($y2 - $y1))*(6378.137);
    return $dist;
}

function compareDistance ($user1, $user2)
{
    return getDistance ($user1['lat'], $user1['lng']) - getDistance ($user2['lat'], $user2['lng']);
}

$mylat = $_SESSION['lat'];
$mylng = $_SESSION['lng'];

$statement = $pdo->prepare("SELECT * FROM users");
$statement->execute();
$users = $statement->fetchAll();

uasort ($users, 'compareDistance');

foreach ($users as $row) { 
    $dist = getDistance ($row['lat'], $row['lng']);
    $distn = floor(round($dist,1) * 2) / 2 ;

    echo $row['username']. ": " . $distn . "km distance";
}