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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);
Output for 7.1.25 - 7.1.33, 7.2.0 - 7.2.33, 7.3.0 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.34, 8.2.0 - 8.2.30, 8.3.0 - 8.3.30, 8.4.1 - 8.4.18, 8.5.0 - 8.5.3
array ( 'Paul' => array ( 'SeasonCounts' => array ( 2014 => 8, 2015 => 3, 2016 => 0, ), ), 'John' => array ( 'SeasonCounts' => array ( 2012 => 4, ), ), )

preferences:
105.86 ms | 1541 KiB | 4 Q