std::ranges::stable_sort
| Defined in header <algorithm>
|
||
| Call signature |
||
template< std::random_access_iterator I, std::sentinel_for<I> S, class Comp = ranges::less, class Proj = std::identity > |
(1) | (since C++20) (constexpr since C++26) |
template< ranges::random_access_range R, class Comp = ranges::less, class Proj = std::identity > |
(2) | (since C++20) (constexpr since C++26) |
Sorts the elements in the range [first, last) in non-descending order. The order of equivalent elements is stable, i.e. guaranteed to be preserved.
A sequence is sorted with respect to a comparator comp if for any iterator it pointing to the sequence and any non-negative integer n such that it + n is a valid iterator pointing to an element of the sequence, std::invoke(comp, std::invoke(proj, *(it + n)), std::invoke(proj, *it) evaluates to false.
The function-like entities described on this page are algorithm function objects (informally known as niebloids), that is:
- Explicit template argument lists cannot be specified when calling any of them.
- None of them are visible to argument-dependent lookup.
- When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.
Contents |
[edit] Parameters
| first, last | - | the iterator-sentinel pair defining the range of elements to sort |
| r | - | the range to sort |
| comp | - | comparison to apply to the projected elements |
| proj | - | projection to apply to the elements |
[edit] Return value
An iterator equal to last.
[edit] Complexity
N·log(N) comparisons, if extra memory is available; where N is ranges::distance(first, last). N·log²(N) comparisons otherwise. Twice as many projections as the number of comparisons in both cases.
[edit] Notes
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_constexpr_algorithms |
202306L |
(C++26) | constexpr stable sorting |
[edit] Possible implementation
This implementation only shows the slower algorithm used when no additional memory is available. See also implementation in MSVC STL and libstdc++.
struct stable_sort_fn { template<std::random_access_iterator I, std::sentinel_for<I> S, class Comp = ranges::less, class Proj = std::identity> requires std::sortable<I, Comp, Proj> constexpr //< since C++26 I operator()(I first, S last, Comp comp = {}, Proj proj = {}) const { auto count = ranges::distance(first, last); auto mid = first + count / 2; auto last_it = first + count; if (count <= 1) return last_it; (*this)(first, mid, std::ref(comp), std::ref(proj)); (*this)(mid, last_it, std::ref(comp), std::ref(proj)); ranges::inplace_merge(first, mid, last_it); return last_it; } template<ranges::random_access_range R, class Comp = ranges::less, class Proj = std::identity> requires std::sortable<ranges::iterator_t<R>, Comp, Proj> constexpr //< since C++26 ranges::borrowed_iterator_t<R> operator()(R&& r, Comp comp = {}, Proj proj = {}) const { return (*this)(ranges::begin(r), ranges::end(r), std::move(comp), std::move(proj)); } }; inline constexpr stable_sort_fn stable_sort{}; |
[edit] Example
#include <algorithm> #include <array> #include <functional> #include <iomanip> #include <iostream> void print(const auto& seq) { for (const auto& elem : seq) std::cout << elem << ' '; std::cout << '\n'; } struct Particle { std::string name; double mass; // MeV friend std::ostream& operator<<(std::ostream& os, const Particle& p) { return os << '\n' << std::left << std::setw(8) << p.name << " : " << p.mass; } }; int main() { std::array s{5, 7, 4, 2, 8, 6, 1, 9, 0, 3}; // sort using the default operator< std::ranges::stable_sort(s); print(s); // sort using a standard library compare function object std::ranges::stable_sort(s, std::ranges::greater()); print(s); // sort using a custom function object struct { bool operator()(int a, int b) const { return a < b; } } customLess; std::ranges::stable_sort(s.begin(), s.end(), customLess); print(s); // sort using a lambda expression std::ranges::stable_sort(s, [](int a, int b) { return a > b; }); print(s); // sort with projection Particle particles[] { {"Electron", 0.511}, {"Muon", 105.66}, {"Tau", 1776.86}, {"Positron", 0.511}, {"Proton", 938.27}, {"Neutron", 939.57} }; print(particles); std::ranges::stable_sort(particles, {}, &Particle::name); //< sorts by name print(particles); std::ranges::stable_sort(particles, {}, &Particle::mass); //< sorts by mass print(particles); }
Output:
0 1 2 3 4 5 6 7 8 9 9 8 7 6 5 4 3 2 1 0 0 1 2 3 4 5 6 7 8 9 9 8 7 6 5 4 3 2 1 0 Electron : 0.511 Muon : 105.66 Tau : 1776.86 Positron : 0.511 Proton : 938.27 Neutron : 939.57 Electron : 0.511 Muon : 105.66 Neutron : 939.57 Positron : 0.511 Proton : 938.27 Tau : 1776.86 Electron : 0.511 Positron : 0.511 Muon : 105.66 Proton : 938.27 Neutron : 939.57 Tau : 1776.86
[edit] See also
| (C++20) |
sorts a range into ascending order (algorithm function object) |
| (C++20) |
sorts the first N elements of a range (algorithm function object) |
| (C++20) |
divides elements into two groups while preserving their relative order (algorithm function object) |
| sorts a range of elements while preserving order between equal elements (function template) |
