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<?php $a = array(array('Holidays' => new DateTime('2018-01-01', new DateTimeZone('Europe/Berlin'))), array('Holidays' => new DateTime('2018-01-26', new DateTimeZone('Australia/Sydney')))); print_r($a); $a = array_map(function ($v) { return $v['Holidays']->format('Y-m-d'); }, $a); print_r($a);

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