一个数组array3 0 = array5 id = int1 name = string1 1 district_name = string9 邵阳县 noise_type = int2 code = string6 430321 1 = array5 id = int2 name = string3 123 district_nam

可以使用循环遍历数组，根据code的值将对应的id添加到新的一维数组中。以下是一种实现方式：

$array = [
    [
        "id" => 1,
        "name" => "1",
        "district_name" => "邵阳县",
        "noise_type" => 2,
        "code" => "430321"
    ],
    [
        "id" => 2,
        "name" => "123",
        "district_name" => "湘潭县",
        "noise_type" => 0,
        "code" => "430321"
    ],
    [
        "id" => 4,
        "name" => "222",
        "district_name" => "开福区",
        "noise_type" => 0,
        "code" => "430105"
    ]
];

$result = [];

foreach ($array as $item) {
    $code = $item['code'];
    $id = $item['id'];
    
    if (!isset($result[$code])) {
        $result[$code] = [];
    }
    
    $result[$code][] = $id;
}

$result = array_values($result);

print_r($result);

输出结果为：

Array
(
    [0] => Array
        (
            [0] => 1
            [1] => 2
        )

    [1] => Array
        (
            [0] => 4
        )
)

最后使用array_values函数将关联数组转换为索引数组，即可得到最终结果。