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<?php $array = [ 0 => 'pens', 1 => 'paper', 2 => 'pencils', 3 => 'lead', 4 => 'trashcans', 5 => 'cars', ]; $string = '2,3,5'; var_dump(implode(',', array_intersect_key($array, array_flip(explode(',', $string)))));
Output for 8.0.1 - 8.0.30, 8.1.0 - 8.1.34, 8.2.0 - 8.2.30, 8.3.0 - 8.3.30, 8.4.1 - 8.4.21, 8.5.0 - 8.5.7
string(17) "pencils,lead,cars"

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