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<?php $array[0]['d'] = 'd1'; $array[0]['a'] = 'a1'; $array[1]['d'] = 'd2'; $array[1]['a'] = 'a2'; $array[2]['d'] = 'd3'; $array[2]['a'] = 'a3'; $array[3]['d'] = 'd1'; $array[3]['a'] = 'a1'; print_r($array); $keys = array_keys($array,"a"); print_r($keys); ?>
Output for 7.0.0 - 7.0.20, 7.1.0 - 7.1.20, 7.2.0 - 7.2.33, 7.3.16 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.27, 8.2.0 - 8.2.17, 8.3.0 - 8.3.4
Array ( [0] => Array ( [d] => d1 [a] => a1 ) [1] => Array ( [d] => d2 [a] => a2 ) [2] => Array ( [d] => d3 [a] => a3 ) [3] => Array ( [d] => d1 [a] => a1 ) ) Array ( )

preferences:
135.08 ms | 404 KiB | 169 Q