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This is available as C\is_sorted_by in the www repository.

Returns true if the given Traversable would be sorted in ascending order after having been Vec\maped with $scalar_func sorted in ascending order

namespace HH\Lib\C;

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

If two neighbouring elements compare equal, this will be considered sorted.

If no $comparator is provided, the <=> operator will be used. This will sort numbers by value, strings by alphabetical order or by the numeric value, if the strings are well-formed numbers, and DateTime/DateTimeImmutable by their unixtime.

To check the order without a mapping function, see C\is_sorted.

If the comparison operator <=> is not useful on Ts and no $comparator is provided, the result of is_sorted_by will not be useful.

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


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


  • bool


$strings = vec[1,2,3,4,5];
$is_sorted_by_result_1 = C\is_sorted_by($strings, $x ==> $x);
echo "First is_sorted_by result: $is_sorted_by_result_1\n";
//Output: First is_sorted_by result: true

$is_sorted_by_result_2 = C\is_sorted_by($strings, $x ==> -$x);
echo "Second is_sorted_by result: $is_sorted_by_result_2\n";
//Output: Second is_sorted_by result: false