Append a new column with a static value to a pre-populated 2d array

$array = array(
    array("a" => 1),
    array("a" => 2)
);

I need to push data to sub array element in $array,

End result must be as follow,

Array (
    [0] => Array (
        [a] => 1
        [b] => 2
    )
    [1] => Array (
        [a] => 2
        [b] => 2
    )
)

I used following ways.

1. foreach ($array as &$a) { 
       $a['b'] = 2;
   }
   

2. $result = array_map("pushdata", $array);
   function pushdata($a) {
       $a['b'] = 2;
   }
   

What is the most suitable and efficient way when $array consists of more than 1000 records?

Here is an example using array_walk() to add a new key b to each sub-array:

$array = array(array('a' => 1), array('a' => 2));
array_walk($array, function(&$item, $key) {
  $item['b'] = 2;
});
print_r($array);
/* outputs:
Array
(
  [0] => Array
  (
      [a] => 1
      [b] => 2
  )
  [1] => Array
  (
      [a] => 2
      [b] => 2
  )
)
*/