[xquery-talk] Collections - family relationships

Michael Kay mike at saxonica.com
Sun Jan 5 13:20:46 PST 2014

On 5 Jan 2014, at 20:59, David Lee <dlee at calldei.com> wrote:

> Given those truths ...
> If you do have a sequence from fn:collection() or another function you *can* find the position of a document in that collection and its 'sibling'
> Note: this may be a horribly inefficient thing to do so buyer beware .... 
> let $c := fn:collection(),
>     $doc := local:pick-a-random-doc( $c ),
>     $prev := $c[ fn:index-of( $c , $doc ) - 1 ]   (: Might be bad to do on the first or  only document :)
>   return $c

This only works if all the documents have distinct string-values.

A more efficient and reliable approach would be

min(for $c at $i in collection() where $c is $doc return $i)

Michael Kay

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