sort_by

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 sorted by some scalar property of each value of the given Traversable, which is computed by the given function

namespace HH\Lib\Vec;

function sort_by<Tv, Ts>(
  Traversable<Tv> $traversable,
  (function(Tv): Ts) $scalar_func,
  ?(function(Ts, Ts): num) $comparator = NULL,
): vec<Tv>;

If the optional comparator function isn't provided, the values will be sorted in ascending order of scalar key.

To sort by the values of the Traversable, see Vec\sort().

Time complexity: O((n log n) * c + n * s), where c is the complexity of the comparator function (which is O(1) if not provided explicitly) and s is the complexity of the scalar function Space complexity: O(n)

Parameters

• Traversable<Tv>$traversable
• (function(Tv): Ts) $scalar_func
• ?(function(Ts, Ts): num) $comparator = NULL

Returns

• vec<Tv>