XQuery to group xml elements - xquery

Question

I was trying some grouping in xquery
<Sheets>
<Sheet>
<ROI>5350</ROI>
<TPI>830</TPI>
</Sheet>
<Sheet>
<ROI>5459</ROI>
<TPI>830</TPI>
</Sheet>
<Sheet>
<ROI>5350</ROI>
<TPI>856</TPI>
</Sheet>
<Sheet>
<ROI>5678</ROI>
<TPI>856</TPI>
</Sheet>
<Sheet>
<ROI>17473</ROI>
<TPI>856</TPI>
</Sheet>
<Sheet>
<ROI>5350</ROI>
<TPI>857</TPI>
</Sheet>
<Sheet>
<ROI>5713</ROI>
<TPI>857</TPI>
</Sheet>
</Sheets>
in my xquery, i want to pass a dynamic value say number 4... i want my xml to group to 4 Sheet elements to one set like
<Sheets>
<set>
<Sheet>
<ROI>5350</ROI>
<TPI>830</TPI>
</Sheet>
<Sheet>
<ROI>5459</ROI>
<TPI>830</TPI>
</Sheet>
<Sheet>
<ROI>5350</ROI>
<TPI>856</TPI>
</Sheet>
<Sheet>
<ROI>5678</ROI>
<TPI>856</TPI>
</Sheet>
</set>
<set>
<Sheet>
<ROI>17473</ROI>
<TPI>856</TPI>
</Sheet>
<Sheet>
<ROI>5350</ROI>
<TPI>857</TPI>
</Sheet>
<Sheet>
<ROI>5713</ROI>
<TPI>857</TPI>
</Sheet>
</set>
</Sheets>
like, group 4 sheets to one set and other 4 to one set and finally rest of them to one set

Answer 1

If you have XQuery 3.0 available, you could use a tumbling window to achieve this quite easily:
xquery version "3.0";
let $group-size := 4 (: set your group size here :)
return
<Sheets>
{
for tumbling window $window in /Sheets/Sheet
start at $start when fn:true()
end at $end when $end - $start eq $group-size - 1
return
<set>{$window}</set>
}
</Sheets>
Otherwise, if you only have XQuery 1.0 available to you, then you can do it with a simple FLWOR expression and positional predicates:
xquery version "1.0";
let $group-size := 4 (: set your group size here :)
return
<Sheets>
{
for $group in (1 to round(count(/Sheets/Sheet) div $group-size) cast as xs:integer)
let $start := (1 * ($group - 1) * $group-size) + 1
let $end := $group * $group-size
return
<set>{/Sheets/Sheet[position() ge $start][position() le $end]}</set>
}
</Sheets>

Answer 2

You could use subsequence() and call a function recursively.
Example...
XML Input
<Sheets>
<Sheet>
<ROI>5350</ROI>
<TPI>830</TPI>
</Sheet>
<Sheet>
<ROI>5459</ROI>
<TPI>830</TPI>
</Sheet>
<Sheet>
<ROI>5350</ROI>
<TPI>856</TPI>
</Sheet>
<Sheet>
<ROI>5678</ROI>
<TPI>856</TPI>
</Sheet>
<Sheet>
<ROI>17473</ROI>
<TPI>856</TPI>
</Sheet>
<Sheet>
<ROI>5350</ROI>
<TPI>857</TPI>
</Sheet>
<Sheet>
<ROI>5713</ROI>
<TPI>857</TPI>
</Sheet>
</Sheets>
XQuery ($groupSize passed as 4)
declare variable $groupSize external;
declare function local:group($set as node()*, $size as xs:integer) as item()* {
<set>{subsequence($set,1,$size)}</set>,
if (count($set)>$groupSize) then
local:group(subsequence($set,$groupSize+1),$groupSize)
else
()
};
<Sheets>{local:group(/*/*,$groupSize)}</Sheets>
XML Output
<Sheets>
<set>
<Sheet>
<ROI>5350</ROI>
<TPI>830</TPI>
</Sheet>
<Sheet>
<ROI>5459</ROI>
<TPI>830</TPI>
</Sheet>
<Sheet>
<ROI>5350</ROI>
<TPI>856</TPI>
</Sheet>
<Sheet>
<ROI>5678</ROI>
<TPI>856</TPI>
</Sheet>
</set>
<set>
<Sheet>
<ROI>17473</ROI>
<TPI>856</TPI>
</Sheet>
<Sheet>
<ROI>5350</ROI>
<TPI>857</TPI>
</Sheet>
<Sheet>
<ROI>5713</ROI>
<TPI>857</TPI>
</Sheet>
</set>
</Sheets>