Thanks to all of you. The group by clause works, while Andy's solution does not seem to produce the right result on my machine. The group by clause, however, moves the elements for the grouping. I was wondering whether it would be possible to count them without moving, and more in general if there is a way to get more control over 2 for-loops combined, so that once a condition is satisfied it is possible to stop a certain repetition.

Hi Joseph,
You could see how XQuery update (http://docs.basex.org/wiki/Update) performs...

let $src:=<c>
<a>red</a>
<a>red</a>
<a>blue</a>
<a>green</a>
<a>green</a>
</c>

return copy $result:=$src
          modify ( for $a in $result/a
        return insert node attribute { 'n' } { 1+count($a/preceding-sibling::a[.=$a])} into $a)
         return $result

/Andy

On 27 January 2017 at 11:23, Marco Lettere <m.lettere@gmail.com> wrote:

Hi Joseph,
what about this?

let $input :=
<c>
<a>red</a>
<a>red</a>
<a>blue</a>
<a>green</a>
<a>green</a>
</c>

return
<c>{
for $a in $input/*
let $t := $a/text()
group by $t
return
for $a2 at $pos in $a
return <a n="{$pos}">{$a2/text()}</a>
}</c>

Ciao,
M.

On 27/01/2017 09:08, meumapple wrote:

Hi,

I have a structure like this:

<c>
<a>red</a>
<a>red</a>
<a>blue</a>
<a>green</a>
<a>green</a>
</c>

And I would like to get:

<c>
<a n="1">red</a>
<a n="2">red</a>
<a n="1">blue</a>
<a n="1">green</a>
<a n="2">green</a>
</c>

I have tried with two for loops after having identified the distinct-values(). This is in principle correct but it takes too long (I have many distinct values and a elements), because I cannot exit the for loop as soon as I get a match. I have been able to get the result with the window clause and then counting the elements of the window with a nested for-loop: is there an alternative solution? Thanks.

Joseph