hugo/docs/content/en/functions/collections/D.md

title, description, categories, keywords, params

title	description	categories	keywords	params
collections.D	Returns a sorted slice of unique random integers based on a given seed, count, and maximum value.		random	functions_and_methods aliases returnType signatures []int collections.D SEED N HIGH

{{< 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.

Objective	Seed example
Consistent result	42
Different result on each call	int time.Now.UnixNano
Same result per day	time.Now.YearDay
Same result per page	hash.FNV32a .Path
Different result per page per day	hash.FNV32a (print .Path time.Now.YearDay)