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<?php $array = [['a', 1], ['b', 1], ['c',2], ['d',2]]; $result = []; foreach ($array as $row) { $result[$row[1]][] = $row; } var_export($result); echo "\n---\n"; var_export( array_reduce( $array, function ($carry, $row) { $carry[$row[1]][] = $row; return $carry; } ) );
Output for 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 - 8.3.4, 8.3.6 - 8.3.7
array ( 1 => array ( 0 => array ( 0 => 'a', 1 => 1, ), 1 => array ( 0 => 'b', 1 => 1, ), ), 2 => array ( 0 => array ( 0 => 'c', 1 => 2, ), 1 => array ( 0 => 'd', 1 => 2, ), ), ) --- array ( 1 => array ( 0 => array ( 0 => 'a', 1 => 1, ), 1 => array ( 0 => 'b', 1 => 1, ), ), 2 => array ( 0 => array ( 0 => 'c', 1 => 2, ), 1 => array ( 0 => 'd', 1 => 2, ), ), )
Output for 8.3.5
Warning: PHP Startup: Unable to load dynamic library 'sodium.so' (tried: /usr/lib/php/8.3.5/modules/sodium.so (libsodium.so.23: cannot open shared object file: No such file or directory), /usr/lib/php/8.3.5/modules/sodium.so.so (/usr/lib/php/8.3.5/modules/sodium.so.so: cannot open shared object file: No such file or directory)) in Unknown on line 0 array ( 1 => array ( 0 => array ( 0 => 'a', 1 => 1, ), 1 => array ( 0 => 'b', 1 => 1, ), ), 2 => array ( 0 => array ( 0 => 'c', 1 => 2, ), 1 => array ( 0 => 'd', 1 => 2, ), ), ) --- array ( 1 => array ( 0 => array ( 0 => 'a', 1 => 1, ), 1 => array ( 0 => 'b', 1 => 1, ), ), 2 => array ( 0 => array ( 0 => 'c', 1 => 2, ), 1 => array ( 0 => 'd', 1 => 2, ), ), )

preferences:
135.14 ms | 403 KiB | 154 Q