Perhaps comparing the count of all @to values with the count of the
union of all @to values:

count(map/*/@to) eq count(union(map/*/@to))

which assumes, of course, that you don't have full identical duplicates.

-W


On 05/11/2012, Costello, Roger L. <costello@xxxxxxxxx> wrote:
> Hi Folks,
>
> I need a good XPath expression which checks that no two websites have the
> same username.
>
> Here is a map between websites and usernames:
>
>     <map>
>         <singletonMap from="Amazon"           	to="BasketballKing" />
>         <singletonMap from="Apple"            	to="RandomGamer" />
>         <singletonMap from="Ebay"             	to="CornFoo" />
>         <singletonMap from="Google"           	to="LatenightRevolution" />
>         <singletonMap from="Microsoft"        	to="OldTrue" />
>         <singletonMap from="VirginAtlantic"   	to="TheSinger" />
>     </map>
>
> In that example no two websites have the same username.
>
> I created an XPath expression which does the job, but I suspect there is a
> simpler expression. Here is my attempt:
>
> empty(for $i in map/*/@to return map/*[@to eq $i][2])
>
> Would you provide a simpler (more efficient, more elegant) version please?
>
> /Roger