When you say "table", it looks like you mean "hash", right? The order of elements in a hash is not fixed except as an (unreliable) side effect.

This recipe for implementing sparse arrays using hashes might help with what you want.

On the other hand, if the Element_<number>s are all consecutive, you might be better off ditching hashes altogether and using a plain array. The previous-element problem becomes trivial, though searching an array for a known value is less simple.