XSLT Reference

random-number-generator()

XSLT 3.0 higher-order function

Returns a deterministic pseudo-random number generator as a map, optionally seeded for reproducible results.

Syntax

random-number-generator(seed?)

Description

random-number-generator() returns a map containing a pseudo-random double in [0, 1), a permutation function, and a next function that produces the next generator state. Because the output is deterministic for a given seed, transformations remain reproducible while still generating random-looking values.

The returned map has three entries:

"number" — an xs:double in [0, 1)
"next" — a zero-argument function returning the next generator map
"permute" — a function that permutes a sequence pseudo-randomly

Parameters

Parameter	Type	Required	Description
`seed`	xs:anyAtomicType?	No	Optional seed value for reproducibility. Omitting gives an implementation-defined seed.

Return value

map(xs:string, item()) — a map with keys "number", "next", and "permute".

Examples

Generating a sequence of random numbers

Stylesheet:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="3.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:xs="http://www.w3.org/2001/XMLSchema">

  <xsl:output method="xml" indent="yes"/>

  <xsl:template match="/">
    <xsl:variable name="rng1" select="random-number-generator(42)"/>
    <xsl:variable name="rng2" select="$rng1('next')()"/>
    <xsl:variable name="rng3" select="$rng2('next')()"/>
    <randoms seed="42">
      <n><xsl:value-of select="format-number($rng1('number'), '0.0000')"/></n>
      <n><xsl:value-of select="format-number($rng2('number'), '0.0000')"/></n>
      <n><xsl:value-of select="format-number($rng3('number'), '0.0000')"/></n>
    </randoms>
  </xsl:template>
</xsl:stylesheet>

Output (values depend on implementation but are deterministic for seed 42):

<randoms seed="42">
  <n>0.7275</n>
  <n>0.1234</n>
  <n>0.5891</n>
</randoms>

Shuffling a sequence with permute

Stylesheet:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="3.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:xs="http://www.w3.org/2001/XMLSchema">

  <xsl:output method="xml" indent="yes"/>

  <xsl:template match="/">
    <xsl:variable name="rng" select="random-number-generator(99)"/>
    <xsl:variable name="items" select="('red', 'green', 'blue', 'yellow', 'purple')"/>
    <xsl:variable name="shuffled" select="$rng('permute')($items)"/>
    <shuffled>
      <xsl:for-each select="$shuffled">
        <color><xsl:value-of select="."/></color>
      </xsl:for-each>
    </shuffled>
  </xsl:template>
</xsl:stylesheet>

Output (deterministic for seed 99):

<shuffled>
  <color>blue</color>
  <color>yellow</color>
  <color>red</color>
  <color>purple</color>
  <color>green</color>
</shuffled>

Notes

The function is pure: the same seed always produces the same sequence, making transformations reproducible.
Without a seed, the implementation may use a random or time-based seed.
The "permute" entry produces a uniformly random permutation of the supplied sequence.
Chain ('next')() calls to advance the generator state without mutating any variable.