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<?php $lol = [ ['for' => '$T4', 'deps' => ['$T3'] ], ['for' => '$T3', 'deps' => ['$T2'] ], ['for' => '$T1', 'deps' => [] ], ['for' => '$T2', 'deps' => ['$T1'] ], ]; uasort($lol, function($a, $b){ if(in_array($a['for'], $b['deps'])) return -1; return 0; }); print_r($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 ( [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 ) ) )
Output for 5.5.24 - 5.5.35, 5.6.8 - 5.6.28
Array ( [3] => Array ( [for] => $T2 [deps] => Array ( [0] => $T1 ) ) [2] => Array ( [for] => $T1 [deps] => Array ( ) ) [1] => Array ( [for] => $T3 [deps] => Array ( [0] => $T2 ) ) [0] => Array ( [for] => $T4 [deps] => Array ( [0] => $T3 ) ) )

preferences:
169.48 ms | 403 KiB | 197 Q