php function to group a list of dictionaries by a common key.

grouper.php

<?php

// I find myself grouping a lot of data... heres a quick helper function to do just that =]

function grouper($data, $key_to_group_by, $key_to_group_unfound='unfound', $unset_key_from_data=false) {
    $grouped_results = array();
    foreach ( $data as $k => $value ) {
        $value_key = isset($value[$key_to_group_by]) ? $value[$key_to_group_by] : $key_to_group_unfound;
        if ( !isset($grouped_results[$value_key]) ) {
            $grouped_results[$value_key] = array();
        }
        if ( $unset_key_from_data == true && $value_key !== $key_to_group_unfound ) {
            unset($value[$key_to_group_by]);
        }
        $grouped_results[$value_key][] = $value;
    }
    return $grouped_results;
}

/*
Example:

$dataset = array(
    array(
        'name' => 'Robin',
        'favorite_color' => 'red',
        'more_data' => 'some'
    ),
    array(
        'name' => 'Jason',
        'favorite_color' => 'orange',
        'more_data' => 'other'
    ),
    array(
        'name' => 'Cody',
        'favorite_color' => 'red',
        'more_data' => 'piece'
    ),
    array(
        'name' => 'Shelly',
        'favorite_color' => 'yellow',
        'more_data' => 'of'
    ),
    array(
        'name' => 'Jessica',
        'favorite_color' => 'orange',
        'more_data' => 'random'
    ),
    array(
        'name' => 'Matt',
        'favorite_color' => 'yellow',
        'more_data' => 'data'
    ),
    array(
        'name' => 'Rachel',
        'favorite_color' => 'orange',
        'more_data' => 'that'
    ),
    array(
        'name' => 'Jessica',
        'favorite_color' => 'red',
        'more_data' => 'doesnt matter'
    ),
);

$results = grouper($test_data['dataset'], $test_data['key']);
print_r($results);
Array
(
    [red] => Array
        (
            [0] => Array
                (
                    [name] => Robin
                    [favorite_color] => red
                    [more_data] => some
                )

            [1] => Array
                (
                    [name] => Cody
                    [favorite_color] => red
                    [more_data] => piece
                )

            [2] => Array
                (
                    [name] => Jessica
                    [favorite_color] => red
                    [more_data] => doesnt matter
                )

        )

    [orange] => Array
        (
            [0] => Array
                (
                    [name] => Jason
                    [favorite_color] => orange
                    [more_data] => other
                )

            [1] => Array
                (
                    [name] => Jessica
                    [favorite_color] => orange
                    [more_data] => random
                )

            [2] => Array
                (
                    [name] => Rachel
                    [favorite_color] => orange
                    [more_data] => that
                )

        )

    [yellow] => Array
        (
            [0] => Array
                (
                    [name] => Shelly
                    [favorite_color] => yellow
                    [more_data] => of
                )

            [1] => Array
                (
                    [name] => Matt
                    [favorite_color] => yellow
                    [more_data] => data
                )

        )

)
*/