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run code in 200+ php & hhvm versions
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<?php $arr = [ [ 'days' => [ 'day_id' => '2016-11-23,2016-11-24', ], ], [ 'days' => [ 'day_id' => '2016-11-25,', ], ], [ 'days' => [ 'day_id' => '', ], ], [ 'days' => [ 'day_id' => '2016-11-27,2016-11-28', ], ], ]; function reduce_func($carry, $item){ if (isset($item['days']) && !empty($item['days']['day_id'])){ $carry += count(array_unique(array_filter(explode(',', $item['days']['day_id'])))); } return $carry; } $result = array_reduce($arr, "reduce_func", 0); var_dump($result);
based on adcTK
Output for 5.6.0 - 7.3.0beta1
int(5)