如何在Laravel中将数组内对象的值转换为指定键名的关联数组？

一、先修正原查询的错误 #

你的原查询最后一个union存在两处错误：表别名使用D但仍用p引用字段，且where条件错误指向C，导致结果重复且顺序不符。修正后的查询如下：

$filter = ["A","B","C","D"];
if(user()->hasRole('admin')){
    $projects = DB::table('projects AS p')
        ->select(DB::raw('count(p.id) as count'))
        ->where('p.alphabet','=','A')
        ->union(DB::table('projects AS p')
            ->select(DB::raw('count(p.id) as count'))
            ->where('p.alphabet','=','B'))
        ->union(DB::table('projects AS p')
            ->select(DB::raw('count(p.id) as count'))
            ->where('p.alphabet','=','C'))
        ->union(DB::table('projects AS p')
            ->select(DB::raw('count(p.id) as count'))
            ->where('p.alphabet','=','D'));
}

不过这种多次union的写法效率较低，更推荐用group by一次性统计，直接得到目标格式：

$filter = ["A","B","C","D"];
if(user()->hasRole('admin')){
    // 按alphabet分组统计已有数据
    $counts = DB::table('projects AS p')
        ->select('p.alphabet', DB::raw('count(p.id) as count'))
        ->whereIn('p.alphabet', $filter)
        ->groupBy('p.alphabet')
        ->pluck('count', 'alphabet')
        ->toArray();

    // 补全filter中未统计到的字母，默认count为0
    $result = array_merge(array_fill_keys($filter, 0), $counts);
}

二、现有结果数组转换方法 #

如果已经拿到原查询返回的对象数组，用Laravel集合工具可以快速转换：

$originalArray = $projects->get()->toArray();
$filter = ["A","B","C","D"];

// 提取所有count值并与filter组合成关联数组
$counts = collect($originalArray)->pluck('count')->toArray();
$result = array_combine($filter, $counts);

// 若原数组顺序与期望不符，手动指定映射关系
// $result = [
//     'A' => $originalArray[0]->count,
//     'B' => $originalArray[1]->count,
//     'C' => $originalArray[3]->count,
//     'D' => $originalArray[2]->count,
// ];

也可以用集合的mapWithKeys链式处理：

$result = collect($originalArray)
    ->zip($filter)
    ->mapWithKeys(function ($item) {
        return [$item[1] => $item[0]->count];
    })
    ->toArray();

注意点 #

• 若原查询结果顺序和$filter不匹配，需手动对应键值或调整查询逻辑保证顺序一致。
• 分组统计的方式比多次union性能更优，数据量大时差异明显。

内容的提问来源于stack exchange，提问作者aliii