Question about keys

[Dennis Brown]

All,

I have a two dimensional array:  array[x,y]
I need to get the unique x keys into a list, there are about 20  
unique ones, but they are dynamically created names (not numbers).
The y keys have tens of thousands of elements.

Is there a simple way to extract the unique x without iterating  
through all the tens of thousands of keys?

I could restructure my code so that I keep a list of unique keys as I  
create them, but this is more complex and could get out of sync since  
I create the elements from many different places in the code.

I could also have a second array that keeps some of the information  
without as many entries.

However, I would prefer keeping everything in one place (it is a  
global) if I can, but I can't think of an easy and fast method.

Thanks,
Dennis