PHP Arrays - Separate Identical Values

Question

Is there any good or standard way of doing this?

Take the following example:

$values = array(
    'blue'
    , 'blue'    
    , 'blue'
    , 'blue'
    , 'green'
    , 'red'
    , 'yellow'
    , 'yellow'
     , 'purple'
    , 'purple'
    , 'purple'
);

I need it to be separated so no two identical values are touching (unless there is no possible solution -- in which case either generating an error, returning false or anything else is acceptable).

Here's the above array (done by hand) but how I am trying to change it:

$values = array(
    'blue'
    , 'purple'
    , 'green'
    , 'purple'
    , 'blue'
    , 'red'
    , 'blue'
    , 'yellow'
    , 'blue'
    , 'yellow'
    , 'purple'
)

The values won't necessarily be in order in the beginning -- that was just for simplicities sake.

Any ideas? Any code to get me started in the right direction?

Answer 1

This function should do the trick:

function uniq_sort($arr){
    if(!count($arr))
        return array();

    $counts = array_count_values($arr);
    arsort($counts);
    while(NULL !== ($key = key($counts)) && $counts[$key]){
        if(isset($prev) && $prev == $key){
            next($counts);
            $key = key($counts);
            if($key === NULL)
                return false;
        }
        $prev = $result[] = $key;

        $counts[$key]--;
        if(!$counts[$key])
            unset($counts[$key]);

        arsort($counts);
        reset($counts);
    }
    return $result;
}

Example usage:

$values = array('blue', 'blue', 'blue', 'blue', 'green', 'red', 'yellow', 'yellow', 'purple', 'purple', 'purple');
print_r(uniq_sort($values));

$values = array('a', 'b', 'b');
print_r(uniq_sort($values));

$values = array(1);
print_r(uniq_sort($values));

$values = array(1, 1, 1, 1, 2, 3, 4);
print_r(uniq_sort($values));

$values = array(1, 1, 1, 1, 2, 3);
var_dump(uniq_sort($values));

And output:

Array
(
    [0] => blue
    [1] => purple
    [2] => blue
    [3] => yellow
    [4] => blue
    [5] => purple
    [6] => blue
    [7] => purple
    [8] => red
    [9] => yellow
    [10] => green
)
Array
(
    [0] => b
    [1] => a
    [2] => b
)
Array
(
    [0] => 1
)
Array
(
    [0] => 1
    [1] => 3
    [2] => 1
    [3] => 4
    [4] => 1
    [5] => 2
    [6] => 1
)
bool(false)