Question

Currently I am trying to restructure a multidimensional array that is the result of a database query. The goal is to finally encode the array as JSON as follows, but the php function i have written isn’t working (see code at end):

desiredJSONoutput = {"TypeA":[
    {"1":[
        {"TypeB":[4,5]},
        {"TypeC":[7,8,4]}]},
    {"2":[
        {"TypeB":[2,3]},
        {"TypeC":[6]}]},
    {"4":[
        {"TypeB":[33,12]},
        {"TypeC":[908]}]}]}

Database structure is:

fromType    fromID      toType      toID
-----------------------------------------------------
TypeA       1       TypeB       4
TypeA       1       TypeB       5
TypeA       1       TypeC       7
TypeA       1       TypeC       8
TypeA       1       TypeC       4
TypeA       2       TypeB       2
TypeA       2       TypeB       3
TypeA       2       TypeC       6
TypeA       2       TypeB       33
TypeA       2       TypeB       12
TypeA       2       TypeC       908

the result of my current sql query is this php array:

Array
(
    Array
    (
        ['fromType'] => 'TypeA'
        ['fromID'] => '1'
        ['toType'] => 'TypeB'
        ['toID'] => '4'  
    )
    Array
    (
        ['fromType'] => 'TypeA'
        ['fromID'] => '1'
        ['toType'] => 'TypeB'
        ['toID'] => '5'  
    )
    Array
    (
        ['fromType'] => 'TypeA'
        ['fromID'] => '1'
        ['toType'] => 'TypeC'
        ['toID'] => '7'  
    )
    Array
    (
        ['fromType'] => 'TypeA'
        ['fromID'] => '1'
        ['toType'] => 'TypeC'
        ['toID'] => '8'  
    )
    Array
    (
        ['fromType'] => 'TypeA'
        ['fromID'] => '1'
        ['toType'] => 'TypeC'
        ['toID'] => '4'  
    )
    Array
    (
        ['fromType'] => 'TypeA'
        ['fromID'] => '2'
        ['toType'] => 'TypeB'
        ['toID'] => '2'  
    )
    Array
    (
        ['fromType'] => 'TypeA'
        ['fromID'] => '2'
        ['toType'] => 'TypeB'
        ['toID'] => '3'  
    )
    Array
    (
        ['fromType'] => 'TypeA'
        ['fromID'] => '2'
        ['toType'] => 'TypeC'
        ['toID'] => '6'  
    )
    Array
    (
        ['fromType'] => 'TypeA'
        ['fromID'] => '3'
        ['toType'] => 'TypeB'
        ['toID'] => '33'  
    )
    Array
    (
        ['fromType'] => 'TypeA'
        ['fromID'] => '3'
        ['toType'] => 'TypeB'
        ['toID'] => '12'  
    )
    Array
    (
        ['fromType'] => 'TypeA'
        ['fromID'] => '3'
        ['toType'] => 'TypeC'
        ['toID'] => '908'  
    )
)

and the restructured array i need before encoding to JSON I think is:

Array
    (
        ['TypeA'] => Array
            (
                ['1'] => Array
                    (
                        ['TypeB'] => Array
                            (
                                [0] => 4
                                [1] => 5
                            )
                        ['TypeC'] => Array
                            (
                                [0] => 7
                                [1] => 8
                                [2] => 4
                            )
                    )
                ['2'] => Array
                    (
                        ['TypeB'] => Array
                            (
                                [0] => 2
                                [1] => 3
                            )
                        ['TypeC'] => Array
                            (
                                [0] => 6
                            )
                    )
                ['3'] => Array
                    (
                        ['TypeB'] => Array
                            (
                                [0] => 33
                                [1] => 12
                            )
                        ['TypeC'] => Array
                            (
                                [0] => 908
                            )
                    )
            )  
    )

I am not sure why the PHP code as follows is not doing the trick to restructure the returned php array to the structure I want:

class Utilities {
    public function linksReEncode($rowsArray) {
        $result = array();

        foreach ($rowsArray as $row) {

            $fromtype = $row['fromtype'];
            $fromID = $row['fromID'];
            $toType = $row['toType'];
            $toID = $row['toID'];

            $arr = $result[$fromType][$fromID][$toType];

            array_push($arr, $toID);
        }
    }
}

EDIT
based on further research and the first answer from @Waygood here’s the function that i am now using and which is working. I wonder if all the checking for existing keys is necessary and if this is the most economical way to achieve this

public function linksReEncode($rows) {
        $result = array();

        foreach ($rows as $row) {

            $fromType = $row['fromType'];
            $fromID = $row['fromID'];
            $toType = $row['toType'];
            $toID = $row['toID'];

            if(!array_key_exists($fromType, $result))
                $result[$fromType] = array();

            if(!array_key_exists($fromID, $result[$fromType]))
                $result[$fromType][$fromID] = array();

            if(!array_key_exists($toType, $result[$fromType][$fromID]))
                $result[$fromType][$fromID][$toType] = array();

            array_push($result[$fromType][$fromID][$toType], $toID);

        }
        return $result;
    }

Answer 1

you are just redefining $arr within each loop, not altering $result

change:

$arr = $result[$fromType][$fromID][$toType];
array_push($arr, $toID);

to:

$result[$fromType][$fromID][$toType][]=$toID;