<?php foreach ($a as $key => $row) { $id[$key] = $row[0]; }
Standard input is empty
Array
(
[0] => Array
(
[0] => idA
[1] => usernameA
)
[1] => Array
(
[0] => idB
[1] => usernameB
)
[2] => Array
(
[0] => idC
[1] => usernameC
)
)