Online PHP editor | refs for ftYfO

<?php $array = [ 1 => [ [ 'class' => 'Advanced Hip Hop Ages 10+', 'session' => 0, 'start' => 1436902200, 'end' => 1436905800, 'capacity' => null, 'students' => 1 ], [ 'class' => 'Intermediate Hip Hop Ages 9+', 'session' => 0, 'start' => 1436899500, 'end' => 1436902200, 'capacity' => null, 'students' => 1 ], [ 'class' => 'Beginning Pointe Ages 10+', 'session' => 0, 'start' => 1436896800, 'end' => 1436899500, 'capacity' => null, 'students' => 1 ], [ 'class' => 'Int/Adv Ballet Ages 10+', 'session' => 0, 'start' => 1436889600, 'end' => 1436896800, 'capacity' => 15, 'students' => 1 ], [ 'class' => 'Beginning Ballet 8+ year olds', 'session' => 0, 'start' => 1436884200, 'end' => 1436891400, 'capacity' => 15, 'students' => 1 ] ], 2 => [ [ 'class' => 'Intermediate Technique/Progressions Ages 9+', 'session' => 0, 'start' => 1436899500, 'end' => 1436904900, 'capacity' => null, 'students' => 1 ], [ 'class' => 'Int/Adv Tap Ages 9+', 'session' => 0, 'start' => 1436895900, 'end' => 1436899500, 'capacity' => null, 'students' => 1 ], [ 'class' => 'Beginning Jazz/Contemporary Technique Ages 8+', 'session' => 0, 'start' => 1436887800, 'end' => 1436893200, 'capacity' => null, 'students' => 1 ] ], 3 => [ [ 'class' => 'Int/Adv Jazz 9+', 'session' => 0, 'start' => 1436893200, 'end' => 1436898600, 'capacity' => null, 'students' => 1 ], [ 'class' => 'Int/Adv Ballet Barre Ages 9+', 'session' => 0, 'start' => 1436886000, 'end' => 1436889600, 'capacity' => null, 'students' => 1 ] ] ]; array_walk($array, fn(&$a1) => usort($a1, fn($a2, $b2) => $a2['start'] <=> $b2['start'])); var_export($array);