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This is available as Vec\sort_by in the www repository.

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)


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


  • vec<Tv>