CODEWITHSUNDEEP
randomxquerysequencemarklogic
s.e
s.e

Reputation: 271

Marklogic: How to return a set of items from a sequence randomly (random sample)?

Let us assume that we have a sequence s:=('a','b','c','d','e'). I want to return a random sample consist of three items from this sequence. How to do so in Marklogic? Note: The sequence that I've used is an example. I'm dealing with large sequence.

Upvotes: 2

Views: 304

Answers (1)

Jens Erat
Jens Erat

Reputation: 38702

One possible way is to repeatedly pull a single value using a recursive function.

declare function local:draw-n($sequence, $n) {
  if ($n > 0)
  then
    let $index := 1 + xdmp:random(count($sequence))
    return ($sequence[$index], local:draw-n($sequence[
      position() < $index or position() > $index
    ], $n - 1))
  else
    ()
};

local:draw-n(('a','b','c','d','e'), 3)

There might be more efficient ways for large sequences, though (like generating three random numbers, making sure they're different and using them to select from the sequence).

declare function local:n-different-random-values($values, $n, $max) {
  if (count($values) eq $n)
  then $values
  else
    let $values := ($values, 1 + xdmp:random(count($sequence)))
    return local:n-different-random-values(distinct-values($values), $n, $max)
};

let $sequence := ('a','b','c','d','e')
let $indexes := local:n-different-random-values((), 3, count($sequence))
return $sequence[position() = $indexes]

Upvotes: 4

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