[Solved] php convert mulitdimentional array

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One option is to use array_reduce to group the array into an associative array and use subjectId as the key. Use array_values to convert the associative array into a simple array.

$result = array_reduce($arr, function($c, $v){
    if ( !isset( $c[$v['subjectId']] ) ) $c[$v['subjectId']] = array( 'subjectId'=> $v['subjectId'], 'subjectName' => $v['subjectName'], 'chapters' => array() );
    $c[$v['subjectId']]['chapters'][] = array( 'chapterId' => $v['chapterId'], 'chapterName' => $v['chapterName']);

    return $c;
}, array());

$result = array_values( $result );

This will result to:

Array
(
    [0] => Array
        (
            [subjectId] => 13
            [subjectName] => Chemistry
            [chapters] => Array
                (
                    [0] => Array
                        (
                            [chapterId] => 1
                            [chapterName] => Chem 1
                        )

                    [1] => Array
                        (
                            [chapterId] => 2
                            [chapterName] => Chem 2
                        )

                )

        )

    [1] => Array
        (
            [subjectId] => 14
            [subjectName] => Mathematics
            [chapters] => Array
                (
                    [0] => Array
                        (
                            [chapterId] => 5
                            [chapterName] => Math 1
                        )

                    [1] => Array
                        (
                            [chapterId] => 6
                            [chapterName] => Math 2
                        )

                )

        )

)

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solved php convert mulitdimentional array