PHP中关联数组的多条件排序：按值降序，再按键升序

<?php
$foodByCategory = [
    "Vegetable" => 2,
    "Fruit" => 1,
    "Fish" => 5,
    "Drinks" => 1,
    "Meat" => 2,
    "Desert" => 3
];

arsort($foodByCategory);

print_r($foodByCategory);
/*
输出:
Array
(
    [Fish] => 5
    [Desert] => 3
    [Meat] => 2
    [Vegetable] => 2
    [Fruit] => 1
    [Drinks] => 1
)
*/
?>

$foodByCategory = [
    "Vegetable" => 2,
    "Fruit" => 1,
    "Fish" => 5,
    "Drinks" => 1,
    "Meat" => 2,
    "Desert" => 3
];

Array
(
    [Fish] => 5
    [Desert] => 3
    [Meat] => 2      // 值与Vegetable相同，但键M < V
    [Vegetable] => 2
    [Drinks] => 1    // 值与Fruit相同，但键D < F
    [Fruit] => 1
)

<?php
$foodByCategory = [
    "Vegetable" => 2,
    "Fruit" => 1,
    "Fish" => 5,
    "Drinks" => 1,
    "Meat" => 2,
    "Desert" => 3
];

// 1. 转换数据结构
$foodList = [];
foreach ($foodByCategory as $category => $count) {
    $foodList[] = [
        "id" => $category,
        "count" => $count
    ];
}

// 2. 使用 usort 进行多条件排序
usort($foodList, function($a, $b) {
    // 主要排序条件：按 'count' 降序
    $cmp = $b["count"] <=> $a["count"]; // 使用 spaceship operator (<=>)

    // 如果 count 相等，则进行次要排序：按 'id' 升序
    if ($cmp === 0) {
        return $a["id"] <=> $b["id"];
    }

    return $cmp;
});

print_r($foodList);

/*
输出:
Array
(
    [0] => Array
        (
            [id] => Fish
            [count] => 5
        )

    [1] => Array
        (
            [id] => Desert
            [count] => 3
        )

    [2] => Array
        (
            [id] => Meat
            [count] => 2
        )

    [3] => Array
        (
            [id] => Vegetable
            [count] => 2
        )

    [4] => Array
        (
            [id] => Drinks
            [count] => 1
        )

    [5] => Array
        (
            [id] => Fruit
            [count] => 1
        )
)
*/

// 如果需要，可以将结果转换回关联数组形式
$sortedFoodByCategory = [];
foreach ($foodList as $item) {
    $sortedFoodByCategory[$item['id']] = $item['count'];
}

print_r($sortedFoodByCategory);
/*
输出:
Array
(
    [Fish] => 5
    [Desert] => 3
    [Meat] => 2
    [Vegetable] => 2
    [Drinks] => 1
    [Fruit] => 1
)
*/
?>

<?php
$foodByCategory = [
    "Vegetable" => 2,
    "Fruit" => 1,
    "Fish" => 5,
    "Drinks" => 1,
    "Meat" => 2,
    "Desert" => 3
];

// 1. 分离键和值
$categories = array_keys($foodByCategory);
$counts = array_values($foodByCategory);

// 2. 使用 array_multisort 进行多重排序
// 第一个排序条件：按 counts 降序 (SORT_DESC)
// 第二个排序条件：按 categories 升序 (SORT_ASC)
array_multisort($counts, SORT_DESC, SORT_NUMERIC, // 主要排序：值降序，数值类型
                $categories, SORT_ASC, SORT_STRING); // 次要排序：键升序，字符串类型

// 3. 重建关联数组
$sortedFoodByCategory = array_combine($categories, $counts);

print_r($sortedFoodByCategory);
/*
输出:
Array
(
    [Fish] => 5
    [Desert] => 3
    [Meat] => 2
    [Vegetable] => 2
    [Drinks] => 1
    [Fruit] => 1
)
*/
?>