HH\Lib\Keyset\filter

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This is available as Keyset\filter in the www repository.

Returns a new keyset containing only the values for which the given predicate returns true

namespace HH\Lib\Keyset;

function filter<Tv as arraykey>(
  Traversable<Tv> $traversable,
  ?(function(Tv): bool) $value_predicate = NULL,
): keyset<Tv>;

The default predicate is casting the value to boolean.

To remove null values in a typechecker-visible way, see Keyset\filter_nulls().

Time complexity: O(n * p), where p is the complexity of $value_predicate Space complexity: O(n)

Parameters

  • Traversable<Tv>$traversable
  • ?(function(Tv): bool) $value_predicate = NULL

Returns

  • keyset<Tv>

Examples

$result = Keyset\filter(keyset[1,2,3,4], $val ==> $val%2==0);
print_r($result);
//result: keyset[2,4]

$result = Keyset\filter(keyset[1,2,3,4], $val ==> $val==0);
print_r($result);
//result: keyset[]

$result = Keyset\filter(keyset[1,2,3,4],  $val ==> $val == $val);
print_r($result);
//result: keyset[1,2,3,4]