First Option

It was not very clear what you wanted, and the transformation of the original data into your "filtered" array did not seem to me exactly what you wanted by its description. I think the result you're looking for looks something like this:

Array (
    [41] => Array ( // Agrupa todos com codreg 41
        [0] => stdClass Object
        (
            [anomes] => 201601
            [codreg] => 41
            [nomreg] => PR
            [codcin] => 1
            [nomcin] => OUTROS
            [valven] => 6835.7000
            [qtdven] => 1078.8000
        )
    )
    [42] => Array ( //agrupa todos com codreg 42
        [0] => stdClass Object
        (
            [anomes] => 201601
            [codreg] => 42
            [nomreg] => SC
            [codcin] => 1
            [nomcin] => OUTROS
            [valven] => 3129.0000
            [qtdven] => 366.6200
        )

        [1] => stdClass Object
        (
            [anomes] => 201601
            [codreg] => 42
            [nomreg] => SC
            [codcin] => 2
            [nomcin] => PECAS
            [valven] => 346.9100
            [qtdven] => 73.6600
        )
    )
)

For this you would need a function like this:

function groupByCodReg($inputArray) {
    $resultMap = [];

    foreach($inputArray as $data) {
        if(!isset($resultMap[$data->codreg])) {
            $resultMap[$data->codreg] = []; 
        }

        $resultMap[$data->codreg][] = $data;    
    }

    return $resultMap;
}

Second Option

Maybe you want to add the values of the arrays in a common key to use in some graph. That would make sense what you tried to do with the data. This way the expected result would look like this:

array(2) {
    ["PR"]=> array(2) {
        [0]=> float(6835.7)
        [1]=> float(0)
    }
    ["SC"]=> array(2) {
        [0]=> float(3129)
        [1]=> float(346.91)
    }
}

For this you could use something like:

function aggregateValvenByNomreg($inputArray) {
    $resultMap = [];

    foreach($inputArray as $data) {
        if(!isset($resultMap[$data->nomreg])) {
            $resultMap[$data->nomreg] = [];
        }

        $resultMap[$data->nomreg][] = $data->valven;
    }

    // completa arrays com 0
    $maiorComprimento = getLengthier($resultMap);
    foreach($resultMap as $key => $value) {
        while(count($resultMap[$key]) < $maiorComprimento) {
            $resultMap[$key][] = 0.0;
        }
    }

    return $resultMap;
}

function getLengthier($array) {
    $max = 0;

    foreach($array as $data) {
        $length = count($data);
        if($length > $max) $max = $length;
    }

    return $max;
}

  

Follow a Repl.it link with the code working for you to verify.    > > > Example Here