XQuery question

Am 20.05.2013 um 14:51 schrieb Marco Lettere <m.lettere at websynapsis.com>: > Hello all, > sorry this email is not properly basex specific but rather XQuery related. > What is the most correct, most efficient in general best way of treating sequences sequentially? > In particular I have an XML describing a sequence of set operations that have to be applied sequentially to the contained sequences of <tem/>s resulting into a final set represented by a sequence of <item/>s. > Unfortunately they are expressed as siblings (flat) rather than dependent nodes (nested hierarchy) which could be handled easily with recursion. > As an example the following sequence shall add the first three items to the empty set then cut down the resulting set to only contain item 2 and 3 and finally remove item 2 from the set resulting in a final set containing only item 3. > > <set operator="UNION"> > <item name="1"/> > <item name="2"/> > <item name="3"/> > </set> > <set operator="INTERSECT"> > <item name="2"/> > <item name="3"/> > <item name="4"/> > <item name="5"/> > </set> > <set operator="DIFFERENCE"> > <item name="2"/> > </set> > > I'd prefer to not have to alter the input data structure. > Thanks a lot for any help, > M. > _______________________________________________ > BaseX-Talk mailing list > BaseX-Talk at mailman.uni-konstanz.de > https://mailman.uni-konstanz.de/mailman/listinfo/basex-talk

On 05/20/2013 03:44 PM, Jens Erat wrote: > hi Marco, > > using recursion is easily possible (and the only way to solve that problem without using maps), just write a small XQuery function like > > declare function local:interprete($operations as item()*, $set as item()*) as item()* { > let $op := head($operations) > let $ops := tail($operations) > let $intermediate := > switch($op/@operator) > case "UNION" return ($set, $op/item[not(@name = $set/@name)]) > case "INTERSECT" return $set[@name = $op/item/@name] > case "DIFFERENCE" return $set[not(@name = $op/item/@name)] > default return error() > return > if ($ops) > then > local:interprete($ops, $intermediate) > else $intermediate > }; > > Which you would call using `local:interpret(//set, ())`. I guess the code should be small enough to be self-explaining. I seems to work, but I didn't test with much more than the input you provided, better do some additional tests on production data before using it. > > If you want to compare whole nodes instead of their name attribute, use `fn:deep-equal()` instead of the name comparisons. You will have to use some explicit loop, [quantified expressions] should get handy for that. > > Regards from Lake Constance, Germany, > Jens Erat > > [quantified expressions]: http://www.w3.org/TR/xpath20/#id-quantified-expressions >

Am 20.05.2013 um 16:31 schrieb Marco Lettere <marco.lettere at dedalus.eu>: > Thanks a lot. > I'm really wondering how I was able to overlook "head" and "tail" .... maybe the age .... :-( > > M. > > On 05/20/2013 03:44 PM, Jens Erat wrote: >> hi Marco, >> >> using recursion is easily possible (and the only way to solve that problem without using maps), just write a small XQuery function like >> >> declare function local:interprete($operations as item()*, $set as item()*) as item()* { >> let $op := head($operations) >> let $ops := tail($operations) >> let $intermediate := >> switch($op/@operator) >> case "UNION" return ($set, $op/item[not(@name = $set/@name)]) >> case "INTERSECT" return $set[@name = $op/item/@name] >> case "DIFFERENCE" return $set[not(@name = $op/item/@name)] >> default return error() >> return >> if ($ops) >> then >> local:interprete($ops, $intermediate) >> else $intermediate >> }; >> >> Which you would call using `local:interpret(//set, ())`. I guess the code should be small enough to be self-explaining. I seems to work, but I didn't test with much more than the input you provided, better do some additional tests on production data before using it. >> >> If you want to compare whole nodes instead of their name attribute, use `fn:deep-equal()` instead of the name comparisons. You will have to use some explicit loop, [quantified expressions] should get handy for that. >> >> Regards from Lake Constance, Germany, >> Jens Erat >> >> [quantified expressions]: http://www.w3.org/TR/xpath20/#id-quantified-expressions >> > > _______________________________________________ > BaseX-Talk mailing list > BaseX-Talk at mailman.uni-konstanz.de > https://mailman.uni-konstanz.de/mailman/listinfo/basex-talk

On 05/20/2013 04:35 PM, Jens Erat wrote: > You don't really need them, they're just syntactical sugar making the code more readable for everybody familiar with functional programming. > > - `head($sequence)` could be written as `$sequence[1]` > - `tail($sequence)` could be written as `$sequence[position()>1]` >