How does one iterate over a sequence in xquery by twos?

Question

I want to iterate over a sequence in xquery and grab 2 elements at a time. What is the easiest way to do this?

Answer 1

I guess three options could be:

for $item at $index in $items
  return
  if ($item mod 2 = 0) then
    ($items[$index - 1], $items[$index])
  else
    ()

and another option might be to use mod and the index of the item:

for $index in 1 to $items div 2
  return
  ($items[($index - 1)*2+1] , $items[($index)*2])

or

for $index in (1 to fn:count($items))[. mod 2 = 0]
  return
  ($items[$index - 1] , $items[$index])

Answer 2

for $item at $index in $items return ( if ($index mod 2 eq 0) then ( $items[xs:integer(xs:integer($index) - 1)], $items[xs:integer($index)] ) else () )

Answer 3

let $s := ("a","b","c","d","e","f")

for $i in 1 to xs:integer(count($s) div 2)
return
<pair>
   {($s[$i*2 - 1],$s[$i*2])} 
</pair>

returns

<pair>a b</pair>
<pair>c d</pair>
<pair>e f</pair>