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<?php $season_data = [ 'Paul' => [ 'Season' => [2014, 2015, 2016] ], 'John' => [ 'Season' => [2012] ] ]; $appearance_data = [ 'Paul' => [ 'Appearance'=> [ 2014, 2014, 2014, 2014, 2014, 2014, 2014, 2014, 2015, 2015, 2015 ] ], 'John' => [ 'Appearance' => [ 2012, 2012, 2012, 2012 ] ] ]; foreach ($season_data as $person => $data) { foreach ($data['Season'] as $year) { $result[$person]['SeasonCounts'][$year] = sizeof(array_filter( $appearance_data[$person]['Appearance'], function($v) use ($year) { return $v == $year; })); } } var_export($result);

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