Group duplicate array keys in a multidimensional array into subarray

arrays, grouping, html-lists, multidimensional-array, php

Solution

This should do it, it's not exactly what you want but I don't see a reason why you'd need to index the resulting array numerically, and then by artist.

$source = array(
    array('Michael Jackson' => 'Thriller'),
    array('Michael Jackson' => 'Rock With You'),
    array('Teddy Pendergrass' => 'Love TKO'),
    array( 'ACDC' => 'Back in Black')
);

$result = array();

foreach($source as $item) {
    $artist = key($item);
    $album = current($item);

    if(!isset($result[$artist])) {
        $result[$artist] = array();
    }
    $result[$artist][] = $album;
}

And you can loop the `$result` array and build your HTML like this:

foreach($result as $artist => $albums) {
    echo '<h2>'.$artist.'</h2>';
    echo '<ul>';
    foreach($albums as $album) {
        echo '<li>'.$album.'</li>';
    }
    echo '</ul>';
}

Which would result in a similar list that you described.

Problem

I have a multidimensional array called `$songs`, which outputs the following: ``` Array ( [0] => Array ( [Michael Jackson] => Thriller ) [1] => Array ( [Michael Jackson] => Rock With You ) [2] => Array ( [Teddy Pendergrass] => Love TKO ) [3] => Array ( [ACDC] => Back in Black ) ) ``` I would like to merge the arrays which have duplicate keys, so I can get the following: ``` Array ( [0] => Array ( [Michael Jackson] => Array ( [0] => Thriller [1] => Rock With You ) ) [1] => Array ( [Teddy Pendergrass] => Love TKO ) [2] => Array ( [ACDC] => Back in Black ) ) ``` How do I do this? Bonus points for giving me the code to output the array like: ``` <h2>Michael Jackson</h2> <ul> <li>Thriller</li> <li>Rock With You</li> </ul> <h2>Teddy Pendergrass</h2> <ul> <li>Love TKO</li> </ul> <h2>ACDC</h2> <ul> <li>Back in Black</li> </ul> ```

Original source