Online PHP editor | output for 5RnUC

<?php $second_names = ['Cars', 'Bikes', 'Trucks']; $premiumCatArraySets = [ [ 'primary-category' => 'Automobiles', 'secondary-category' => 'Cars', 'tertiary-category' => 'Fiat Punto' ], [ 'primary-category' => 'Automobiles', 'secondary-category' => 'Cars', 'tertiary-category' => 'BMW' ], [ 'primary-category' => 'Automobiles', 'secondary-category' => 'Bikes', 'tertiary-category' => 'Honda' ], [ 'primary-category' => 'Automobiles', 'secondary-category' => 'Trucks', 'tertiary-category' => 'Iveco' ] , [ 'primary-category' => 'Automobiles', 'secondary-category' => 'Cars', 'tertiary-category' => 'Mercedes' ] , [ 'primary-category' => 'Automobiles', 'secondary-category' => 'Cars', 'tertiary-category' => 'Toyota' ] ]; $output = []; foreach($premiumCatArraySets as $key => $value){ if(in_array($value["secondary-category"],$second_names)){ if(!isset($output[$value["secondary-category"]])){ $output[$value["secondary-category"]] = []; } $output[$value["secondary-category"]][] = $value["tertiary-category"]; } } foreach($output as $key => $value){ echo '<h2>'.$key."</h2>"; echo implode(",",$value)."<br/>"; } print_r($output);