PHP ksort

1.例子一：

<?php
/**
 * 根据 c1 对元素排序
 */
$arrays = [
    'b' => [
        'c1' => 10,
        'c2' => 5,
    ],
    'a' => [
        'c1' => 5,
        'c2' => 8,
    ],
    'c' => [
        'c1' => 9,
        'c2' => 10,
    ],
    'e' => [
        'c1' => 5,
        'c2' => 10,
    ],
];

$t = [];
$c = 'c1';

foreach($arrays as $key => $array){
    $cv = $array[$c];
    if(!isset($t[$cv])){
        $t[$cv] = [];
    }
    $t[$cv][] = $key;
}
ksort($t);
print_r($t);
foreach($t as $v){
    if(is_array($v)){
        foreach($v as $y){
            $s[$y] = $arrays[$y];
        }
    }else{
        $s[$y] = $arrays[$y];
    }
}
print_r($s);