Mine

I have two arrays: $val_one:
array(16) {
  [20070115]=>
  array(4) {
    [0]=>
    string(4) "1283"
    [1]=>
    string(5) "12282"
    [2]=>
    string(8) "61429943"
    [3]=>
    string(3) "434"
  }
.....

and $val_two:

array(12) {
  [20070201]=>
  array(4) {
    [0]=>
    string(4) "1424"
    [1]=>
    string(5) "13737"
    [2]=>
    string(8) "65988051"
    [3]=>
    string(3) "489"
  }
...

using array_merge($val_one, $val_two) gives me:

array(28) {
  [0]=>
  array(4) {
    [0]=>
    string(4) "1283"
    [1]=>
    string(5) "12282"
    [2]=>
    string(8) "61429943"
    [3]=>
    string(3) "434"
  }
  [1]=>
  array(4) {
    [0]=>
    string(4) "1393"
    [1]=>
    string(5) "14405"
    [2]=>
    string(8) "68428466"
    [3]=>
    string(3) "462"
  }

apparently the keys are missing because they are numeric and re-assigned. How, if I want to keep them numeric, would I combine the two arrays so that the keys are preserved?