比较数组中的类似值并使用其他值生成新数组

Question

This is my current array and i want to compare similar user_id and generate new array with all the related questions. Like as we can see in below example that User 1 have Question 1 and Question 2 in array and at next we can see that User 1 have Question 4 and Question 5, So i need to combine all the questions and want to generate user wise array.

Array

[0] => Array
    (
        [user_id] => User 1
        [question_1] => Question 1?
        [question_2] => Question 2?

[1] => Array
    (
        [user_id] => User 2
        [question_1] => Question 2?
        [question_2] => Question 3?
    )

[2] => Array
    (
        [user_id] => User 3
        [question_1] => Question 3?
        [question_2] => Question 1?
    )

[3] => Array
    (
        [user_id] => User 4
        [question_1] => Question 1?
        [question_2] => Question 2?
    )

[4] => Array
    (
        [user_id] => User 5
        [question_1] => Question 2?
        [question_2] => Question 3?
    )

[5] => Array
    (
        [user_id] => User 1
        [question_1] => Question 4?
        [question_2] => Question 5?
    )

[6] => Array
    (
        [user_id] => User 2
        [question_1] => Question 5?
        [question_2] => Question 6?
    )

[7] => Array
    (
        [user_id] => User 3
        [question_1] => Question 6?
        [question_2] => Question 4?
    )

[8] => Array
    (
        [user_id] => User 4
        [question_1] => Question 4?
        [question_2] => Question 5?
    )

[9] => Array
    (
        [user_id] => User 5
        [question_1] => Question 5?
        [question_2] => Question 6?
    )

[10] => Array
    (
        [user_id] => User 1
        [question_1] => Question 7?
        [question_2] => Question 8?
    )

[11] => Array
    (
        [user_id] => User 2
        [question_1] => Question 8?
        [question_2] => 
    )

[12] => Array
    (
        [user_id] => User 3
        [question_1] => 
        [question_2] => Question 7?
    )

[13] => Array
    (
        [user_id] => User 4
        [question_1] => Question 7?
        [question_2] => Question 8?
    )

[14] => Array
    (
        [user_id] => User 5
        [question_1] => Question 8?
        [question_2] => 
    )

)

Here is the example what i want exactly.

[0] = Array
('user_id' => 'User 1',
 'questions' => Array
   (
     'Question 1',
     'Question 2',
     'Question 4',
     'Question 5',
     'Question 7',
     'Question 8'
   )
 )
[1] = Array
('user_id' => 'User 2',
 'questions' => Array
   (
     'Question 2',
     'Question 3',
     'Question 5',
     'Question 6',
     'Question 8'
   )
 )

So any one can help me to generate array like above for all users.

I have tried with below code to find similar value and push it new array.

foreach ($final_array as $master)
    {
        array_push($ques,$master['question_1']);

        array_push($ques,$master['question_2']);

        $temp_array = array('user_id' => $master['user_id'],'questions' => $ques);

        $search = ['user_id' => $master['user_id']];

        $keys1 = array_keys(array_filter($all_array,function ($v) use ($search) { return $v['user_id'] == $search['user_id']; } ) );

        if(isset($keys1[0]))
        {
            $st = $keys1[0];    

            array_push($all_array[$st]['questions'],$master['question_1']);
            array_push($all_array[$st]['questions'],$master['question_2']);
        } 
        else
        {
            array_push($all_array, $temp_array);

        }
    }

And below is the output after applying above code.

Array
(
    [0] => Array
        (
            [user_id] => User 1
            [questions] => Array
                (
                    [0] => Question 1?
                    [1] => Question 2?
                    [2] => Question 4?
                    [3] => Question 5?
                    [4] => Question 7?
                    [5] => Question 8?
                )

        )

    [1] => Array
        (
            [user_id] => User 2
            [questions] => Array
                (
                    [0] => Question 1?
                    [1] => Question 2?
                    [2] => Question 2?
                    [3] => Question 3?
                    [4] => Question 5?
                    [5] => Question 6?
                    [6] => Question 8?
                    [7] => 
                )

        )

    [2] => Array
        (
            [user_id] => User 3
            [questions] => Array
                (
                    [0] => Question 1?
                    [1] => Question 2?
                    [2] => Question 2?
                    [3] => Question 3?
                    [4] => Question 3?
                    [5] => Question 1?
                    [6] => Question 6?
                    [7] => Question 4?
                    [8] => 
                    [9] => Question 7?
                )

        )

    [3] => Array
        (
            [user_id] => User 4
            [questions] => Array
                (
                    [0] => Question 1?
                    [1] => Question 2?
                    [2] => Question 2?
                    [3] => Question 3?
                    [4] => Question 3?
                    [5] => Question 1?
                    [6] => Question 1?
                    [7] => Question 2?
                    [8] => Question 4?
                    [9] => Question 5?
                    [10] => Question 7?
                    [11] => Question 8?
                )

        )

    [4] => Array
        (
            [user_id] => User 5
            [questions] => Array
                (
                    [0] => Question 1?
                    [1] => Question 2?
                    [2] => Question 2?
                    [3] => Question 3?
                    [4] => Question 3?
                    [5] => Question 1?
                    [6] => Question 1?
                    [7] => Question 2?
                    [8] => Question 2?
                    [9] => Question 3?
                    [10] => Question 5?
                    [11] => Question 6?
                    [12] => Question 8?
                    [13] => 
                )

        )

)

Answer 1

You could loop array $items with the questions and first store the user_id to use that later to index in the $result array as the key.

Then unset user_id so we are left with the questions only. Check if the key is already in use in $result. If it is not, create the array structure that you want for user_id and questions and add the first questions array.

If the key already exists, merge the questions array with the existing one.

At the end use array_map and array_unique to remove all the duplicate questions and use array_values to index the array numerically.

$result = [];

foreach ($items as $item) {
    $userId = $item['user_id'];
    unset($item['user_id']);
    if (!array_key_exists($userId, $result)) {
        $result[$userId] = [
            'user_id' => $userId,
            'questions' => array_values($item)
        ];
        continue;
    }
    $result[$userId]['questions'] = array_merge(
        array_values($result[$userId]['questions']),
        array_values($item)
    );
}

$result = array_values(array_map(function($y) {
    $y['questions'] = array_unique($y['questions']);
    return $y;
}, $result));

print_r($result);

Demo