Sample

:::info[Note] This is a point-in-time snapshot of the API documentation from January 2026. Going forward, we will not be maintaining a public copy of these references, and recommend users to refer to the built-in signature helpers available in the Hack LSP instead for complete and up-to-date information. :::

Returns a new vec containing an unbiased random sample of up to $sample_size elements (fewer iff $sample_size is larger than the size of $traversable)

namespace HH\Lib\Vec;

function sample<Tv>(
  Traversable<Tv> $traversable,
  int $sample_size,
): vec<Tv>;

Time complexity: O(n), where n is the size of $traversable Space complexity: O(n), where n is the size of $traversable -- note that n may be bigger than $sample_size

Parameters

• Traversable<Tv>$traversable
• int $sample_size

Returns

• vec<Tv>

Examples

$example_vec = vec[1,2,3,4,5];
$result = Vec\sample($example_vec, 3);
print_r($result);
//result: [2,5,3] OR any 3 elements

$result = Vec\sample($example_vec, 0);
print_r($result);
//result: []

$result = Vec\sample($example_vec, 5);
print_r($result);
//result: [4,5,2,1,3]; All 5 elements