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filter_keys

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 dict containing only the keys for which the given predicate returns true

namespace HH\Lib\Dict;

function filter_keys<Tk as arraykey, Tv>(
  KeyedTraversable<Tk, Tv> $traversable,
  ?(function(Tk): bool) $key_predicate = NULL,
): dict<Tk, Tv>;

The default predicate is casting the key to boolean.

Time complexity: O(n * p), where p is the complexity of $value_predicate (which is O(1) if not provided explicitly) Space complexity: O(n)

Parameters​

Returns​

  • dict<Tk, Tv>