1行に項目の配列が入ってるから項目の配列を行にして、各行に項目の値を入れたい

gistfile1.txt

    public function testRowArrayConvert() {

        $ar = [
            'a' => ['123','123','123','123'],
            'b' => ['123','123','123','123'],
            'c' => ['123','','123','123'],
            'd' => ['123','123',null,'123'],
            'e' => ['123','123','','123'],
            'f' => ['','123','123','123'],
        ];

        $arC = count($ar['a']);
        $arR = [];

        for($i = 0; $i < $arC; $i++) {
            foreach($ar as $key => $array) {
                $arR[$i][$key] = $array[$i];
            }
        }

        self::assertTrue(is_array($arR));
        self::assertTrue(count($arR) === $arC);

        $keyyyyyyyyyyyy = array_keys($ar);

        foreach($keyyyyyyyyyyyy as $key) {
            for($i = 0; $i < count($arR); $i++) {
                self::assertTrue(array_key_exists($key, $arR[$i]));
            }
        }

    }