collections.D

{{< new-in 0.149.0 />}}

The collections.D function returns a sorted slice of unique random integers in the half-open interval [0, HIGH) using the provided SEED value. The number of elements in the resulting slice is N or HIGH, whichever is less.

• N and H must be integers in the closed interval [0, 1000000]
• SEED must be an integer in the closed interval [0, 2^64 - 1]

Return values

Condition|Return value :--|:--|:-- N <= HIGH|A sorted random sample of size N using J. S. Vitter's Method D for sequential random sampling N > HIGH|The full, sorted range [0, HIGH) of size HIGH N == 0|An empty slice N < 0|Error N > 10^6|Error HIGH == 0|An empty slice HIGH < 0|Error HIGH > 10^6|Error SEED < 0|Error {.no-wrap-first-col}

Examples

{{ collections.D 6 7 42 }} → [4, 9, 10, 20, 22, 24, 41]

The example above generates the same random numbers each time it is called. To generate a different set of 7 random numbers in the same range, change the seed value.

{{ collections.D 2 7 42 }} → [3, 11, 19, 25, 32, 33, 38]

When N is greater than HIGH, this function returns the full, sorted range [0, HIGH) of size HIGH:

{{ collections.D 6 42 7 }} → [0 1 2 3 4 5 6] 

A common use case is the selection of random pages from a page collection. For example, to render a list of 5 random pages using the day of the year as the seed value:

<ul>
  {{ $p := site.RegularPages }}
  {{ range collections.D time.Now.YearDay 5 ($p | len) }}
    {{ with (index $p .) }}
      <li><a href="{{ .RelPermalink }}">{{ .LinkTitle }}</a></li>
    {{ end }}
  {{ end }}
</ul>

The construct above is significantly faster than using the collections.Shuffle function.

Seed value

Choosing an appropriate seed value depends on your objective.