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<?php $array = Array ( "field_5abcb693a68bc" => Array ( "0" => Array ( "field_5abcbb1b51ddf" => "mortgage", "field_5ae58a0b58b58" => "", "field_5abcbb1e51de0" => "10", "field_5abcbb2351de2" => "45,654,456", "field_5abcbb6251de3" => "", "field_5abcbb6651de4" => "04/2017", "field_5abcbb6851de5" => "4,454,656", "field_5abcbb6b51de6" => "24/07/2018", "field_5abcbbb351de7" => "657", "field_5abcbbb651de8" => "24/07/2018", "field_5abcbbb851de9" => "15", "field_5abcbbbb51dea"=> "yes" ) ) ); array_walk_recursive( $array, function (&$value) { if (preg_match('/^\d[1-9]\/[1-9][0-9][0-9][0-9]$/',$value)) { $value = '01/' . $value; } } ); var_dump($array);
Output for 5.6.0 - 5.6.40, 7.0.0 - 7.0.33, 7.1.0 - 7.1.33, 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 - 8.1.33, 8.2.0 - 8.2.29, 8.3.0 - 8.3.25, 8.4.1 - 8.4.12
array(1) { ["field_5abcb693a68bc"]=> array(1) { [0]=> array(12) { ["field_5abcbb1b51ddf"]=> string(8) "mortgage" ["field_5ae58a0b58b58"]=> string(0) "" ["field_5abcbb1e51de0"]=> string(2) "10" ["field_5abcbb2351de2"]=> string(10) "45,654,456" ["field_5abcbb6251de3"]=> string(0) "" ["field_5abcbb6651de4"]=> string(10) "01/04/2017" ["field_5abcbb6851de5"]=> string(9) "4,454,656" ["field_5abcbb6b51de6"]=> string(10) "24/07/2018" ["field_5abcbbb351de7"]=> string(3) "657" ["field_5abcbbb651de8"]=> string(10) "24/07/2018" ["field_5abcbbb851de9"]=> string(2) "15" ["field_5abcbbbb51dea"]=> string(3) "yes" } } }

preferences:
106.46 ms | 410 KiB | 5 Q