array - undefined index in sorting php result

Question

I wrote an API where I return questions from one table and all the answers from another related to that question.

As it needs to sort them like multidimensional array I worked with logic but it throws an error on last "foreach",

My code:

 $results = $this->getQuestionRepository()
        ->createQueryBuilder('a')
        ->getQuery()
        ->getResult();

    $questionResults = $results[0];

    $answers = $this->getAnswer($qresults); // gets all of the answers by question

    $mappedQuestions = [];
    foreach ($questionResults as $result){
        $mappedQuestions[$result->getId()];
    }

    foreach ($questions as $question){

        $questionId = $question->getQuestion()->getName();
        $mappedQuestions[$questionId];
    }

    $results[0] = array_values($mappedQuestions);

    return $results;

and it throws:

Notice: Undefined index: Name

and the problem is in

$mappedQuestions[$questionId];

As results in first dump query I get:

results