std::ranges::unique_copy, std::ranges::unique_copy_result
From cppreference.com
1) Copies the elements from the source range
[first, last), to the destination range beginning at result in such a way that there are no consecutive equal elements. Only the first element of each group of equal elements is copied. The ranges
[first, last) and [result, result + N) must not overlap. N =ranges::distance(first, last). Two consecutive elements *(i -1) and *i are considered equivalent if std::invoke(comp, std::invoke(proj, *(i -1)), std::invoke(proj, *i))==true, where
i is an iterator in the range [first +1, last).2) Same as (1), but uses r as the range, as if using ranges::begin(r) as first, and ranges::end(r) as last.
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 source range of elements to process |
| r | - | the source range of elements |
| result | - | the destination range of elements |
| comp | - | the binary predicate to compare the projected elements |
| proj | - | the projection to apply to the elements |
[edit]Return value
{last, result + N}
[edit]Complexity
Exactly N -1 applications of the corresponding predicate comp and no more than twice as many applications of any projection proj.
[edit]Possible implementation
See also the implementations in libstdc++ and MSVC STL (and third-party libraries: cmcstl2, NanoRange, and range-v3).
struct unique_copy_fn {template<std::input_iterator I, std::sentinel_for<I> S, std::weakly_incrementable O, class Proj =std::identity, std::indirect_equivalence_relation<std::projected<I, Proj>> C =ranges::equal_to> requires std::indirectly_copyable<I, O>&&(std::forward_iterator<I>||(std::input_iterator<O>&&std::same_as<std::iter_value_t<I>, std::iter_value_t<O>>)||std::indirectly_copyable_storable<I, O>)constexpr ranges::unique_copy_result<I, O> operator()(I first, S last, O result, C comp ={}, Proj proj ={})const{if(!(first == last)){std::iter_value_t<I> value =*first;*result = value;++result;while(!(++first == last)){auto&& value2 =*first;if(!std::invoke(comp, std::invoke(proj, value2), std::invoke(proj, value))){ value =std::forward<decltype(value2)>(value2);*result = value;++result;}}} return{std::move(first), std::move(result)};} template<ranges::input_range R, std::weakly_incrementable O, class Proj =std::identity, std::indirect_equivalence_relation<std::projected<ranges::iterator_t<R>, Proj>> C =ranges::equal_to> requires std::indirectly_copyable<ranges::iterator_t<R>, O>&&(std::forward_iterator<ranges::iterator_t<R>>||(std::input_iterator<O>&&std::same_as<ranges::range_value_t<R>, std::iter_value_t<O>>)||std::indirectly_copyable_storable<ranges::iterator_t<R>, O>)constexpr ranges::unique_copy_result<ranges::borrowed_iterator_t<R>, O> operator()(R&& r, O result, C comp ={}, Proj proj ={})const{return(*this)(ranges::begin(r), ranges::end(r), std::move(result), std::move(comp), std::move(proj));}}; inlineconstexpr unique_copy_fn unique_copy {}; |
[edit]Example
Run this code
#include <algorithm>#include <cmath>#include <iostream>#include <iterator>#include <list>#include <string>#include <type_traits> void print(constauto& rem, constauto& v){using V =std::remove_cvref_t<decltype(v)>;constexprbool sep{std::is_same_v<typename V::value_type, int>};std::cout<< rem <<std::showpos;for(constauto& e : v)std::cout<< e <<(sep ?" ":"");std::cout<<'\n';} int main(){std::string s1{"The string with many spaces!"}; print("s1: ", s1); std::string s2; std::ranges::unique_copy( s1.begin(), s1.end(), std::back_inserter(s2), [](char c1, char c2){return c1 ==' '&& c2 ==' ';}); print("s2: ", s2); constauto v1 ={-1, +1, +2, -2, -3, +3, -3}; print("v1: ", v1);std::list<int> v2; std::ranges::unique_copy( v1, std::back_inserter(v2), {}, // default comparator std::ranges::equal_to[](int x){return std::abs(x);}// projection); print("v2: ", v2);}
Output:
s1: The string with many spaces! s2: The string with many spaces! v1: -1 +1 +2 -2 -3 +3 -3 v2: -1 +2 -3
[edit]See also
(C++20) | removes consecutive duplicate elements in a range (algorithm function object) |
(C++20)(C++20) | copies a range of elements to a new location (algorithm function object) |
(C++20) | finds the first two adjacent items that are equal (or satisfy a given predicate) (algorithm function object) |
| creates a copy of some range of elements that contains no consecutive duplicates (function template) |
