/**
* @return array
*/
protected function prepareValues()
{
$periods = $this->configuration->getPeriods();
$values = [];
foreach ($periods as $period) {
$values[$period->format($this->configuration->getGroupByDateFormat())] = ['value' => 0, 'meta' => $period->format($this->configuration->getDatePresentationFormat())];
}
return $values;
}
