Ok, I see. Thanks a lot for the great help again! M.
On 28/08/2018 16:05, Christian Grün wrote:
You can use the fn:sort function for that:
for tumbling window $w in sort( db:open("adatabase")[every $f in $filters satisfies $f(.)], (), function($doc) { db:path($doc) } ) ...
Sorting is a blocking operator, though: All documents will need to be checked first in order to tell which one will be the smallest or largest hit.
Best, Christian
On Tue, Aug 28, 2018 at 4:01 PM Marco Lettere m.lettere@gmail.com wrote:
.... and what if, a pervert I know, would like to have the docs also globally ordered by any sort criteria? Any chance of squeezing the order by into this elegant FLOWR? Thanks again. M.
On 28/08/2018 15:41, Christian Grün wrote:
Hi Marco,
Here is a minimized representation of your last query:
for tumbling window $w in db:open("adatabase")[every $f in $filters satisfies $f(.)] start $first at $s when ($s = 1 + ($page - 1) * $count) end $last at $e when $e - $s = $count - 1 return $wCheers, Christian
On Tue, Aug 28, 2018 at 3:27 PM Marco Lettere m.lettere@gmail.com wrote:
Oh, yes. Thank you Martin. That is obviously a good point. The input is a database with several thousands of documents stored in it. The filters are a dynamic sequence of xpath expressions to be applied on the documents expressed as function references. I need to check whether I can compress all this into a simple predicate as you've shown in your example. where clause would have been much more easier in conjunction with the map operator (!) but if it works I'm going to coope with the predicate. Thanks for your suggestion in the meanwhile.
Here a simplified example of my current approach where you could think of $filters as a sequence of boolean functions to be applied to the documents in the db.
let $seq := for $doc in db:open("adatabase") where not(false() = ($filters ! (.($doc))) return $doc let $out := for tumbling window $w in $seq start $first at $s when ($s = 1 + ($page - 1) * $count) end $last at $e when $e - $s = $count - 1 return $wRegards, Marco.
On 28/08/2018 14:19, Martin Honnen wrote:
On 28.08.2018 11:04, Marco Lettere wrote:
here's a question related to XQuery, sorry for being slightly off-topic.
I'm struggling to find a way to combine the windowing clause and FLOWR in order to get a paged result of a subset of items which respect a given filter.
Of course I'm able to get this by first applying the filter to the whole input and then a second FLOWR for the windowing clause.
So what is the filter condition? What is the input sequence?
The closer I get is [1] which is not what I'd need because I get 2,4,6,8,10 as result for page 1 but I'd really want 10 results per page thus 2,4,6,8,10,12,14,16,18,20.
Thanks for any help on this in the meanwhile I'll stick to my naive solution.
Marco.
[1]
let $page := 1 let $count := 10 return for tumbling window $w in (1 to 100) start $first at $s when ($s = 1 + ($page - 1) * $count) end $last at $e when ($e - $s = $count - 1) return $w ! (if (. mod 2 = 0 ) then . else ())
Can't you simply use the filter as a predicate on the expression you use in the windowing for clause?
Does
let $page-size := 10 for tumbling window $page in (1 to 100)[. mod 2 = 0] start at $sp when $sp mod $page-size = 1 end at $np when ($np + 1) mod $page-size = 1 return <page>{$page}</page>
help?
It returns
<page>2 4 6 8 10 12 14 16 18 20</page> <page>22 24 26 28 30 32 34 36 38 40</page> <page>42 44 46 48 50 52 54 56 58 60</page> <page>62 64 66 68 70 72 74 76 78 80</page> <page>82 84 86 88 90 92 94 96 98 100</page>