Adding an element to the beginning of an array without changing other array keys [duplicate]

Question

How can I add an element to the beginning of array without changing array key values in PHP?

Answer 1

To keep numerical keys from being reindexed, you could simply add the arrays together.

Instead of:

array_unshift($arr1, $arr2)

try:

$arr1 = $arr2 + $arr1;

Answer 2

If you use self-assigned (e.g. literal) keys, array_unshift() will do it.
If you use auto-generated (numeric) keys, how should that work? Use '-1' as the new first key?

EDIT:
Thank you to JasonS for pointing out an error in this answer.
ANY numeric key will be re-indexed by array_unshift(), no matter if it was auto-generated or self-assigned - if it's numeric, it'll get scrambled. See the link to the documentation above for details.