count element using Xquery and return the value

Question

my xml data:

<a>
   <book>
        <pub>John</pub>
   </book>
   <book>
        <pub>John</pub>
    </book>
    <book>
         <pub>Mary</pub>
    </book>
</a>

So i want to count number for each and display them

Expected output:

 <result>
         <pub>John</pub>
         <total>2</total>
 </result>
 <result>
         <pub>Mary</pub>
         <total>1</total>
  </result>

But my output:

 <result>
         <pub>John</pub>
         <total>1</total>
 </result>
<result>
         <pub>John</pub>
         <total>1</total>
 </result>
 <result>
         <pub>Mary</pub>
         <total>1</total>
  </result>

code i using :

for $b in /a/book
let $count := count($b/pub)
for $pub in $b/pub
return
     <result> {$pub} <total>{$count}</total></result>

it keep looping the same data but not group it . even i use distinct-values it's still same. what error in my code?

Jens Erat · Accepted Answer · 2014-06-08 16:21:21Z

2

If using an XQuery 3.0 capable XQuery processor, you can also take advantage of the group by flwor statement:

for $book in /a/book
let $publisher := $book/pub
group by $publisher
return
  <result>
    <pub>{ $publisher }</pub>
    <count>{ count($book) }</count>
   </result>

answered Jun 8, 2014 at 16:21

Jens Erat

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Comments

helderdarocha · Accepted Answer · 2014-06-08 16:10:43Z

1

Grouping works using distinct-values. You can count all the books or pubs and filter only the ones that match the current iteration.

This:

let $b := /a/book/pub
  for $pub in distinct-values($b)
      let $count := count($b[. eq $pub])
      return <result>
                <pub>{$pub}</pub> 
                <total>{$count}</total>
             </result>

will produce:

<result>
   <pub>John</pub>
   <total>2</total>
</result>
<result>
   <pub>Mary</pub>
   <total>1</total>
</result>

edited Jun 8, 2014 at 16:10

answered Jun 8, 2014 at 16:04

helderdarocha

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4 Comments

user3664490 Over a year ago

want to understand. what is this code for let $count := count($b[. eq $pub]) why got . inside?

helderdarocha Over a year ago

$pub is the current node (/a/book/pub) in the context of the for loop. $b is a set containing all nodes (total of 3): /a/book/pub[1], /a/book/pub[2] and /a/book/pub[3]. Basically in each iteration of the loop, you compare the current node $pub with all three nodes, and select only the ones which have the same string value as $pub. The . inside the predicate "[...]" represents the node itself (predicates in XPath are contextual). Since I'm relying on the string value. You could also replace the . for node() or text().

helderdarocha Over a year ago

If you remove the predicate [. eq $pub] you should get the total value always (3), since $b doesn't change in the loop. If you use count($pub) you will always get 1, because there is only one pub per iteration of the loop.

user3664490 Over a year ago

so i can change to count($b[text() = $pub/text()])?

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