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<?php $dates = ['2011-04-11', '2011-06-28', '2011-09-26', '2012-01-02', '2012-05-12']; $startdates = [ 10 => '2011-01-01', 20 => '2011-07-01', 30 => '2012-01-01', 40 => '2012-07-01' ]; $enddates = [ 10 => '2011-06-30', 20 => '2011-12-31', 30 => '2012-06-30', 40 => '2012-12-31' ]; foreach ($dates as $date) { foreach ($startdates as $key => $startdate) { if ($date >= $startdate && $date <= $enddates[$key]) { $result[$date] = $key; continue 2; } } $result[$date] = 'out of bounds'; } var_export($result);

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