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<?php $lol = array ( 0 => array ( 'for' => '$T4', 'deps' => array ( 0 => '$T3', ), ), 1 => array ( 'for' => '$T3', 'deps' => array ( 0 => '$T2', ), ), 2 => array ( 'for' => '$T1', 'deps' => array ( ), ), 3 => array ( 'for' => '$T2', 'deps' => array ( 0 => '$T1', ), ), ); uasort($lol, function($a, $b){ return in_array($a['for'], $b['deps']) ? -1 : 1; }); print_r($lol);
Output for 7.0.0 - 7.0.20, 7.1.0 - 7.1.25, 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 - 8.1.28, 8.2.0 - 8.2.18, 8.3.0 - 8.3.6
Array ( [1] => Array ( [for] => $T3 [deps] => Array ( [0] => $T2 ) ) [2] => Array ( [for] => $T1 [deps] => Array ( ) ) [3] => Array ( [for] => $T2 [deps] => Array ( [0] => $T1 ) ) [0] => Array ( [for] => $T4 [deps] => Array ( [0] => $T3 ) ) )
Output for 5.5.24 - 5.5.35, 5.6.8 - 5.6.28
Array ( [3] => Array ( [for] => $T2 [deps] => Array ( [0] => $T1 ) ) [1] => Array ( [for] => $T3 [deps] => Array ( [0] => $T2 ) ) [2] => Array ( [for] => $T1 [deps] => Array ( ) ) [0] => Array ( [for] => $T4 [deps] => Array ( [0] => $T3 ) ) )

preferences:
144.96 ms | 403 KiB | 198 Q