How to add the values for respective elements? - xpath

Question

I have 3 XML structures as below:
a.xml
<Books>
<Book>
<Publisher>ABC Pvt Ltd</Publisher>
<Month>May</Month>
<Year>2016</Year>
<BooksReleased>4</BooksReleased>
</Book>
</Books>
b.xml
<Books>
<Book>
<Publisher>XYZ Pvt Ltd</Publisher>
<Month>April</Month>
<Year>2016</Year>
<BooksReleased>2</BooksReleased>
</Book>
</Books>
c.xml
<Books>
<Book>
<Publisher>ABC Pvt Ltd</Publisher>
<Month>June</Month>
<Year>2016</Year>
<BooksReleased>2</BooksReleased>
</Book>
</Books>
I would like to group these XML by publisher and also need to calculate its total no. of BooksReleased by the publisher for particular year.
required output format:
<TotalCalc>
<PublishedBook>
<Publisher>ABC Pvt Ltd</Publisher>
<no.of books>6</no.of books>
</PublishedBook>
<PublishedBook>
<Publisher>XYZ Pvt Ltd</Publisher>
<no.of books>2</no.of books>
</PublishedBook>
</TotalCalc>
Kindly, help me i tried the following but its not working
typeswitch($Publisher)
case element (ABC Pvt Ltd)
return sum($doc/BooksReleases[$doc/$Publisher = 'ABC Pvt Ltd'])
default return 'unknnown'

Answer 1

It might be possible to use cts:value-tuples to pull up co-occurrences of Publisher and 'BooksReleased', which you can then iterate to aggregate by Publisher. That would scale much better. Something like:
let $aggregates := map:map()
let $_ :=
for $tuple in cts:value-tuples((
cts:element-reference(xs:QName("Publisher")),
cts:element-reference(xs:QName("BooksReleased"))
))
let $values := json:array-values($tuple)
let $pub := $values[1]
let $books as xs:int := $values[2]
return map:put($aggregates, $pub, (map:get($aggregates, $pub), 0)[1] + $books)
return $aggregates
Note thought that this requires indexes on Publisher and BooksReleased, and it is important that each document contains only one (value of) Publisher to prevent cross-products.
I would also consider simply dropping (or ignoring) BooksReleased, and just making sure you save each book as a separate document. You can then use cts:values on Publisher and use cts:frequency on each publisher value to get the number of books for the publishers.
HTH!