Locker\Data\Analytics\Analytics::setInterval PHP Method

    private function setInterval($interval = '')
    {
        $interval = $interval === '' ? 'day' : $interval;
        // Defines the acceptable intervals and their Mongo counterpart.
        $intervals = ['day' => '$dayOfYear', 'dayOfMonth' => '$dayOfMonth', 'dayOfWeek' => '$dayOfWeek', 'week' => '$week', 'hour' => '$hour', 'month' => '$month', 'year' => '$year'];
        // Validates the interval.
        if (!isset($intervals[$interval])) {
            throw new Exceptions\Exception("'{$interval}' is not a valid `interval`.");
        }
        return $intervals[$interval];
    }