Sort and display array values according to a value?

Given the following PHP array:

Array
(
    [0] => Array
        (
            [name] => Restaurant 123
            [city] => Arlington
            [zip] => 22201
        )

    [1] => Array
        (
            [name] => Bar Foo
            [city] => Ballston
            [zip] => 22201开发者_StackOverflow社区
         )
     [2] => Array
        (
            [name] => Restaurant XYZ
            [city] => Ballston
            [zip] => 22201
         )

    [3] => Array
        (
            [name] => Restaurant 321
            [city] => Washington DC
            [zip] => 22201
         )

)

How can I produce a list sorted according to city (alphabetically), so that it would output something like:

Arlington

Restaurant 123

Ballston

Bar Foo

Restaurant XYZ

Washington DC

Restaurant 321

E.G., sorted first by city name alphabetically, and then by venue name, also alphabetically. Also note that it's not given that the restaurant name, nor the cities are alphabetically sorted in the array given.

Write a callback function that you can pass to usort, for example

function compare_venues($a, $b)
{
  return strcmp($a['name'], $b['name']);
}

You can use usort, which enables you to sort an array based on a user-defined comparison function.

Try usort ( http://php.net/manual/en/function.usort.php ) where you can define a custom sort schema like

function cmp($a, $b)
{
    if ($a == $b) {
        return 0;
    }
    return ($a < $b) ? -1 : 1;
}

Looks like theres two parts to what you want - sorting and displaying.

To sort, you want to use usort with small function defining the comparison

$sortFunc = function($a,$b) {return $a['city'] != $b['city'] 
                                 ? $a['city'] > $b['city']
                                 : $a['name'] > $b['name'];};

        // = function($a,$b) {return $a['city'] > $b['city'] || ($a['city'] == $b['city'] && $a['name'] > $b['name']);};
        // = function($a,$b) {return 100*strcmp($a['city'],$b['city']) + strcmp($a['name'],$b['name']);};
usort($arr, $sortFunc);

function displayNamesGroupedByCity($arr)
{
    $lastCity = '';
    foreach($arr as $v)
    {
        if ($v['city'] != $lastCity)
        {
             $lastCity = $v['city'];
             echo "<br /><strong>$lastCity</strong><br />";
        }
        else echo ', ';
        echo $v['name'];
    }
}

displayNamesGroupedByCity($arr);

For the hell of it im going to make things generic

function displayXgroupedByY($arr, $x, $y)
{
    $sortFunc = function($a,$b) use($x,$y) 
                               {return $a[$y] != $b[$y] 
                                 ? $a[$y] > $b[$y]
                                 : $a[$x] > $b[$y];};

    user($arr, $sortFunc);

    $lastCity = '';
    foreach($arr as $v)
    {
        if ($v['city'] != $lastCity)
        {
             $lastCity = $v['city'];
             echo "<br /><strong>$lastCity</strong><br />";
        }
        else echo ', ';
        echo $v['name'];
    }
    return $arr;
}

displayXGroupedByY($arr, 'name', 'city');

user defined sorting should do a work:

http://us2.php.net/manual/en/function.uasort.php