如何将多维数组中的键移动到多个级别？

Question

Explanation

I have an Array with conversations, each conversation may contain one or multiple messages. A message may contain one or multiple attachments, the attachments are bound to a conversation. My goal is to move the attachment(s) to the corresponding message. Here's the pseudo Array:

$conversations = [
        [
            'id' => 'c1',
            'messages' => [
                [
                    'id' => 'm1',
                    'content' => 'Herewith the attachments'
                ],
                [
                    'id' => 'm2',
                    'content' => 'Ah, thanks'
                ],
                [
                    'id' => 'm3',
                    'content' => 'What about the invoice?'
                ],
                [
                    'id' => 'm4',
                    'content' => 'Oh shoot, here it is'
                ]
            ],
            'attachments' => [
                [
                    'id' => 'a1',
                    'message_id' => 'm1',
                    'filename' => 'something.pdf'
                ],
                [
                    'id' => 'a2',
                    'message_id' => 'm1',
                    'filename' => 'somethingelse.pdf'
                ],
                [
                    'id' => 'a3',
                    'message_id' => 'm4',
                    'filename' => 'invoice.pdf'
                ]
            ]
        ]
    ];

I would like to loop through each conversation, if the attachments key is set I would like to bind the attachment to the corresponding message by message_id . How does one do this?

Expected result

$conversations = [
        [
            'id' => 'c1',
            'messages' => [
                [
                    'id' => 'm1',
                    'content' => 'Herewith the attachments',
                    'attachments' => [
                        [
                            'id' => 'a1',
                            'message_id' => 'm1',
                            'filename' => 'something.pdf'
                        ],
                        [
                            'id' => 'a2',
                            'message_id' => 'm1',
                            'filename' => 'somethingelse.pdf'
                        ]
                    ]
                ],
                [
                    'id' => 'm2',
                    'content' => 'Ah, thanks'
                ],
                [
                    'id' => 'm3',
                    'content' => 'What about the invoice?'
                ],
                [
                    'id' => 'm4',
                    'content' => 'Oh shoot, here it is',
                    'attachments' => [
                        [
                            'id' => 'a3',
                            'message_id' => 'm4',
                            'filename' => 'invoice.pdf'
                        ]
                    ]
                ]
            ]
        ]
    ];

Answer 1

I would do something like this: Start with setting the id as key of the array, then add the attachments to that key.

$joint_array = array();

foreach($conversations['messages'] as $x){
    $joint_array[$x['id']] = $x;
}

foreach($conversations['attachments'] as $y){
    $joint_array[$y['message_id']]['attachments'][] = $y;
}

Answer 2

First of all, I would change keys to ids (id should be unique, right?) so items in array will be somewhat accessible. Then moving anything to anything should be simple as well as accessing it without iteration.

foreach($conversations AS $conversation) {
    $indexedMessages = [];

    foreach($conversation['messages'] AS $message) {
        $indexedMessages[$message['id']] = $message;
    }

    foreach($conversation['attachments'] AS $attachment) {
        $indexedMessages[$attachment['message_id']]['attachments'][/* you may put $attachment['id'] here */] = $attachment;
    }

    $result = [
        'id' => $conversation['id'],
        'messages' => $indexedMessages
    ];
}

$result is this:

Array
(
    [id] => c1
    [messages] => Array
        (
            [m1] => Array
                (
                    [id] => m1
                    [content] => Herewith the attachments
                    [attachments] => Array
                        (
                            [0] => Array
                                (
                                    [id] => a1
                                    [message_id] => m1
                                    [filename] => something.pdf
                                )

                            [1] => Array
                                (
                                    [id] => a2
                                    [message_id] => m1
                                    [filename] => somethingelse.pdf
                                )

                        )

                )

            [m2] => Array
                (
                    [id] => m2
                    [content] => Ah, thanks
                )

            [m3] => Array
                (
                    [id] => m3
                    [content] => What about the invoice?
                )

            [m4] => Array
                (
                    [id] => m4
                    [content] => Oh shoot, here it is
                    [attachments] => Array
                        (
                            [0] => Array
                                (
                                    [id] => a3
                                    [message_id] => m4
                                    [filename] => invoice.pdf
                                )

                        )

                )

        )

)