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

namespace HH\Lib\Dict;

function sort_by<Tk as arraykey, Tv, Ts>(
  KeyedTraversable<Tk, Tv> $traversable,
  (function(Tv): Ts) $scalar_func,
  ?(function(Ts, Ts): num) $scalar_comparator = NULL,
): dict<Tk, 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 KeyedTraversable, see Dict\sort().
  • To sort by the keys of the KeyedTraversable, see Dict\sort_by_key().

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​

  • KeyedTraversable<Tk,Tv> $traversable
  • (function(Tv): Ts) $scalar_func
  • ?(function(Ts, Ts): num) $scalar_comparator = NULL

Returns​

  • dict<Tk, Tv>