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 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.
Parameters
| first, last | - | the source range of elements |
| 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 |
Return value
{last, result + N}.
Complexity
Exactly N - 1 applications of the corresponding predicate comp and no more than twice as many applications of any projection proj.
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> or (std::input_iterator<O> && std::same_as<std::iter_value_t<I>, std::iter_value_t<O>>) or 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>> or (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)); } }; inline constexpr unique_copy_fn unique_copy {}; |
Example
Run this code
#include <algorithm> #include <cmath> #include <iostream> #include <iterator> #include <list> #include <string> #include <type_traits> void print(const auto& rem, const auto& v) { using V = std::remove_cvref_t<decltype(v)>; constexpr bool sep {std::is_same_v<typename V::value_type, int>}; std::cout << rem << std::showpos; for (const auto& 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); const auto 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
See also
| (C++20) |
removes consecutive duplicate elements in a range (niebloid) |
| (C++20)(C++20) |
copies a range of elements to a new location (niebloid) |
| (C++20) |
finds the first two adjacent items that are equal (or satisfy a given predicate) (niebloid) |
| creates a copy of some range of elements that contains no consecutive duplicates (function template) |