std::ranges::set_union, std::ranges::set_union_result
Defined in header <algorithm>
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Call signature |
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template< std::input_iterator I1, std::sentinel_for<I1> S1, std::input_iterator I2, std::sentinel_for<I2> S2, |
(1) | (since C++20) |
template< ranges::input_range R1, ranges::input_range R2, std::weakly_incrementable O, class Comp = ranges::less, |
(2) | (since C++20) |
Helper types |
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template<class I1, class I2, class O> using set_union_result = ranges::in_in_out_result<I1, I2, O>; |
(3) | (since C++20) |
Constructs a sorted union beginning at result
consisting of the set of elements present in one or both sorted input ranges [first1, last1)
and [first2, last2)
.
If some element is found m
times in [first1, last1)
and n
times in [first2, last2)
, then all m
elements will be copied from [first1, last1)
to result
, preserving order, and then exactly max(n-m, 0) elements will be copied from [first2, last2)
to result
, also preserving order.
The behavior is undefined if
- the input ranges are not sorted with respect to
comp
andproj1
orproj2
, respectively, or - the resulting range overlaps with either of the input ranges.
comp
.r1
as the first range and r2
as the second range, as if using ranges::begin(r1) as first1
, ranges::end(r1) as last1
, ranges::begin(r2) as first2
, and ranges::end(r2) as last2
.The function-like entities described on this page are niebloids, that is:
- Explicit template argument lists may not be specified when calling any of them.
- None of them is visible to argument-dependent lookup.
- When one of them is found by normal unqualified lookup for the name to the left of the function-call operator, it inhibits argument-dependent lookup.
In practice, they may be implemented as function objects, or with special compiler extensions.
Parameters
first1, last1 | - | iterator-sentinel pair denoting the first input sorted range |
first2, last2 | - | iterator-sentinel pair denoting the second input sorted range |
r1 | - | the first input sorted range |
r2 | - | the second input sorted range |
result | - | the beginning of the output range |
comp | - | comparison to apply to the projected elements |
proj1 | - | projection to apply to the elements in the first range |
proj2 | - | projection to apply to the elements in the second range |
Return value
{last1, last2, result_last}, where result_last is the end of the constructed range.
Complexity
At most 2·(N
1+N
2)-1 comparisons and applications of each projection, where N
1 and N
2 are ranges::distance(first1, last1) and ranges::distance(first2, last2), respectively.
Notes
This algorithm performs a similar task as ranges::merge does. Both consume two sorted input ranges and produce a sorted output with elements from both inputs. The difference between these two algorithms is with handling values from both input ranges which compare equivalent (see notes on LessThanComparable). If any equivalent values appeared n
times in the first range and m
times in the second, ranges::merge would output all n+m occurrences whereas ranges::set_union
would output std::max(n, m) ones only. So ranges::merge outputs exactly (N
1+N
2) values and ranges::set_union
may produce less.
Possible implementation
struct set_union_fn { template< std::input_iterator I1, std::sentinel_for<I1> S1, std::input_iterator I2, std::sentinel_for<I2> S2, std::weakly_incrementable O, class Comp = ranges::less, class Proj1 = std::identity, class Proj2 = std::identity > requires std::mergeable<I1, I2, O, Comp, Proj1, Proj2> constexpr ranges::set_union_result<I1, I2, O> operator()( I1 first1, S1 last1, I2 first2, S2 last2, O result, Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {} ) const { for (; !(first1 == last1 or first2 == last2); ++result) { if (std::invoke(comp, std::invoke(proj1, *first1), std::invoke(proj2, *first2))) { *result = *first1; ++first1; } else if (std::invoke(comp, std::invoke(proj2, *first2), std::invoke(proj1, *first1))) { *result = *first2; ++first2; } else { *result = *first1; ++first1; ++first2; } } auto res1 = ranges::copy(std::move(first1), std::move(last1), std::move(result)); auto res2 = ranges::copy(std::move(first2), std::move(last2), std::move(res1.out)); return {std::move(res1.in), std::move(res2.in), std::move(res2.out)}; } template< ranges::input_range R1, ranges::input_range R2, std::weakly_incrementable O, class Comp = ranges::less, class Proj1 = std::identity, class Proj2 = std::identity > requires std::mergeable<ranges::iterator_t<R1>, ranges::iterator_t<R2>, O, Comp, Proj1, Proj2> constexpr ranges::set_union_result<ranges::borrowed_iterator_t<R1>, ranges::borrowed_iterator_t<R2>, O> operator()( R1&& r1, R2&& r2, O result, Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {} ) const { return (*this)(ranges::begin(r1), ranges::end(r1), ranges::begin(r2), ranges::end(r2), std::move(result), std::move(comp), std::move(proj1), std::move(proj2)); } }; inline constexpr set_union_fn set_union{}; |
Example
#include <algorithm> #include <iostream> #include <iterator> #include <vector> void print(const auto& in1, const auto& in2, auto first, auto last) { std::cout << "{ "; for (const auto& e : in1) { std::cout << e << ' '; } std::cout << "} ∪ { "; for (const auto& e : in2) { std::cout << e << ' '; } std::cout << "} =\n{ "; while (!(first == last)) { std::cout << *first++ << ' '; } std::cout << "}\n\n"; } int main() { std::vector<int> in1, in2, out; in1 = {1, 2, 3, 4, 5}; in2 = { 3, 4, 5, 6, 7}; out.resize(in1.size() + in2.size()); const auto ret = std::ranges::set_union(in1, in2, out.begin()); print(in1, in2, out.begin(), ret.out); in1 = {1, 2, 3, 4, 5, 5, 5}; in2 = { 3, 4, 5, 6, 7}; out.clear(); out.reserve(in1.size() + in2.size()); std::ranges::set_union(in1, in2, std::back_inserter(out)); print(in1, in2, out.cbegin(), out.cend()); }
Output:
{ 1 2 3 4 5 } ∪ { 3 4 5 6 7 } = { 1 2 3 4 5 6 7 } { 1 2 3 4 5 5 5 } ∪ { 3 4 5 6 7 } = { 1 2 3 4 5 5 5 6 7 }
See also
(C++20) |
computes the difference between two sets (niebloid) |
(C++20) |
computes the intersection of two sets (niebloid) |
computes the symmetric difference between two sets (niebloid) | |
(C++20) |
merges two sorted ranges (niebloid) |
(C++20) |
returns true if one sequence is a subsequence of another (niebloid) |
computes the union of two sets (function template) |