For a recent project I needed to sort an associative array by value first, and then by key if a particular value appeared multiple times. I wrote this function to accomplish the task. Note that the parameters default to sort ascending on both keys and values, but allow granular control over each.

<?php
function aksort(&$array,$valrev=false,$keyrev=false) {
  if ($valrev) { arsort($array); } else { asort($array); }
    $vals = array_count_values($array);
    $i = 0;
    foreach ($vals AS $val=>$num) {
        $first = array_splice($array,0,$i);
        $tmp = array_splice($array,0,$num);
        if ($keyrev) { krsort($tmp); } else { ksort($tmp); }
        $array = array_merge($first,$tmp,$array);
        unset($tmp);
        $i = $num;
    }
}

// Example
$tmp = array('ca'=>1,'cb'=>2,'ce'=>1,'pa'=>2,'pe'=>1);

// Standard asort
asort($tmp);
print_r($tmp);

// Sort value ASC, key ASC
aksort($tmp);
print_r($tmp);

// Sort value DESC, key ASC
aksort($tmp,true);
print_r($tmp);

// Sort value DESC, key DESC
aksort($tmp,true,true);
print_r($tmp);

// Results
Array
(
    [pe] => 1
    [ca] => 1
    [ce] => 1
    [cb] => 2
    [pa] => 2
)
Array
(
    [ca] => 1
    [ce] => 1
    [pe] => 1
    [cb] => 2
    [pa] => 2
)
Array
(
    [cb] => 2
    [pa] => 2
    [ca] => 1
    [ce] => 1
    [pe] => 1
)
Array
(
    [pa] => 2
    [cb] => 2
    [pe] => 1
    [ce] => 1
    [ca] => 1
)