Difference between revisions of "cpp/algorithm/ranges/partial sort copy"
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| − | Copies the first {{tt|N}} elements from the source range {{tt|[first, last)}}, as if it was partially sorted with respect to {{tt|comp}} and {{tt|proj1}}, into the destination range {{tt|[result_first, result_first + N)}}, where {{ | + | Copies the first {{tt|N}} elements from the source range {{tt|[first, last)}}, as if it was partially sorted with respect to {{tt|comp}} and {{tt|proj1}}, into the destination range {{tt|[result_first, result_first + N)}}, where {{mathjax-or|1=\(\scriptsize N = \min{(L_1, L_2)}\)|2=N = min(L₁, L₂)}}, {{mathjax-or|\(\scriptsize L_1\)|L₁}} is equal to {{c|ranges::distance(first, last)}}, and {{mathjax-or|\(\scriptsize L_2\)|L₂}} is equal to {{c|ranges::distance(result_first, result_last)}}. |
The order of equal elements is ''not'' guaranteed to be preserved. | The order of equal elements is ''not'' guaranteed to be preserved. | ||
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{{par | comp | comparison to apply to the projected elements}} | {{par | comp | comparison to apply to the projected elements}} | ||
{{par | proj1 | projection to apply to the elements of source range}} | {{par | proj1 | projection to apply to the elements of source range}} | ||
| − | {{par | proj2 | projection to apply to the elements of destination range | + | {{par | proj2 | projection to apply to the elements of destination range}} |
{{par end}} | {{par end}} | ||
===Return value=== | ===Return value=== | ||
| − | An object equal to {{ | + | An object equal to {{c|{last, result_first + N} }}. |
===Complexity=== | ===Complexity=== | ||
| − | At most {{ | + | At most {{mathjax-or|\(\scriptsize L_1 \cdot \log{(N)}\)|L₁•log(N)}} comparisons and {{mathjax-or|\(\scriptsize 2 \cdot L_1 \cdot \log{(N)}\)|2•L₁•log(N)}} projections. |
===Possible implementation=== | ===Possible implementation=== | ||
Revision as of 09:26, 9 July 2021
| 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::random_access_iterator I2, std::sentinel_for<I2> S2, |
(1) | (since C++20) |
| template< ranges::input_range R1, ranges::random_access_range R2, class Comp = ranges::less, class Proj1 = std::identity, |
(2) | (since C++20) |
| Helper types |
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| template<class I, class O> using partial_sort_copy_result = ranges::in_out_result<I, O>; |
(3) | (since C++20) |
Copies the first N elements from the source range [first, last), as if it was partially sorted with respect to comp and proj1, into the destination range [result_first, result_first + N), where N = min(L₁, L₂), L₁ is equal to ranges::distance(first, last), and L₂ is equal to ranges::distance(result_first, result_last).
The order of equal elements is not guaranteed to be preserved.
1) The source range elements are projected using the function object
proj1, and the destination elements are projected using the function object proj2.2) Same as (1), but uses
r as the source range and result_r as the destination range, as if using ranges::begin(r) as first, ranges::end(r) as last, ranges::begin(result_r) as result_first, and ranges::end(result_r) as result_last.The function-like entities described on this page are 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.
In practice, they may be implemented as function objects, or with special compiler extensions.
Contents |
Parameters
| first, last | - | iterator-sentinel defining the source range to copy from |
| r | - | the source range to copy from |
| result_first, result_last | - | iterator-sentinel defining the destination range |
| result_r | - | the destination range |
| comp | - | comparison to apply to the projected elements |
| proj1 | - | projection to apply to the elements of source range |
| proj2 | - | projection to apply to the elements of destination range |
Return value
An object equal to {last, result_first + N}.
Complexity
At most L₁•log(N) comparisons and 2•L₁•log(N) projections.
Possible implementation
struct partial_sort_copy_fn { template< std::input_iterator I1, std::sentinel_for<I1> S1, std::random_access_iterator I2, std::sentinel_for<I2> S2, class Comp = ranges::less, class Proj1 = std::identity, class Proj2 = std::identity > requires std::indirectly_copyable<I1, I2> && std::sortable<I2, Comp, Proj2> && std::indirect_strict_weak_order<Comp, std::projected<I1, Proj1>, std::projected<I2, Proj2>> constexpr ranges::partial_sort_copy_result<I1, I2> operator()( I1 first, S1 last, I2 result_first, S2 result_last, Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {} ) const { if (result_first == result_last) { return {std::move(ranges::next(std::move(first), std::move(last))), std::move(result_first)}; } auto out_last {result_first}; // copy first N elements for (; !(first == last or out_last == result_last); ++out_last, ++first) { *out_last = *first; } // convert N copied elements into a max-heap ranges::make_heap(result_first, out_last, comp, proj2); // process the rest of the input range (if any), preserving the heap property for (; first != last; ++first) { if (std::invoke(comp, std::invoke(proj1, *first), std::invoke(proj2, *result_first))) { // pop out the biggest item and push in a newly found smaller one ranges::pop_heap(result_first, out_last, comp, proj2); *(out_last - 1) = *first; ranges::push_heap(result_first, out_last, comp, proj2); } } // first N elements in the output range is still a heap - convert it into a sorted range ranges::sort_heap(result_first, out_last, comp, proj2); return {std::move(first), std::move(out_last)}; } template< ranges::input_range R1, ranges::random_access_range R2, class Comp = ranges::less, class Proj1 = std::identity, class Proj2 = std::identity > requires std::indirectly_copyable<ranges::iterator_t<R1>, ranges::iterator_t<R2>> && std::sortable<ranges::iterator_t<R2>, Comp, Proj2> && std::indirect_strict_weak_order<Comp, std::projected<ranges::iterator_t<R1>, Proj1>, std::projected<ranges::iterator_t<R2>, Proj2>> constexpr ranges::partial_sort_copy_result<ranges::borrowed_iterator_t<R1>, ranges::borrowed_iterator_t<R2>> operator()( R1&& r, R2&& result_r, Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {} ) const { return (*this)(ranges::begin(r), ranges::end(r), ranges::begin(result_r), ranges::end(result_r), std::move(comp), std::move(proj1), std::move(proj2)); } }; inline constexpr partial_sort_copy_fn partial_sort_copy{}; |
Example
Run this code
#include <algorithm> #include <forward_list> #include <functional> #include <iostream> #include <ranges> #include <string_view> #include <vector> void print(std::string_view rem, std::ranges::input_range auto const& v) { for (std::cout << rem; const auto& e : v) std::cout << e << ' '; std::cout << '\n'; } int main() { const std::forward_list source{4, 2, 5, 1, 3}; print("Write to the smaller vector in ascending order: ", ""); std::vector dest1{10, 11, 12}; print("const source list: ", source); print("destination range: ", dest1); std::ranges::partial_sort_copy(source, dest1); print("partial_sort_copy: ", dest1); print("Write to the larger vector in descending order:", ""); std::vector dest2{10, 11, 12, 13, 14, 15, 16}; print("const source list: ", source); print("destination range: ", dest2); std::ranges::partial_sort_copy(source, dest2, std::greater{}); print("partial_sort_copy: ", dest2); }
Output:
Write to the smaller vector in ascending order: const source list: 4 2 5 1 3 destination range: 10 11 12 partial_sort_copy: 1 2 3 Write to the larger vector in descending order: const source list: 4 2 5 1 3 destination range: 10 11 12 13 14 15 16 partial_sort_copy: 5 4 3 2 1 15 16
See also
| (C++20) |
sorts the first N elements of a range (niebloid) |
| (C++20) |
sorts a range into ascending order (niebloid) |
| (C++20) |
sorts a range of elements while preserving order between equal elements (niebloid) |
| (C++20) |
turns a max heap into a range of elements sorted in ascending order (niebloid) |
| (C++20) |
creates a max heap out of a range of elements (niebloid) |
| (C++20) |
adds an element to a max heap (niebloid) |
| (C++20) |
removes the largest element from a max heap (niebloid) |
| copies and partially sorts a range of elements (function template) |
