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std::ranges::unique_copy, std::ranges::unique_copy_result

From cppreference.com
< cpp‎ | algorithm‎ | ranges
 
 
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. std::ranges::copy, std::ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
(C++11)(C++11)(C++11)
(C++17)
Modifying sequence operations
Partitioning operations
Sorting operations
(C++11)
Binary search operations
Set operations (on sorted ranges)
Heap operations
(C++11)
Minimum/maximum operations
(C++11)
(C++17)

Permutations
Numeric operations
Operations on uninitialized storage
(C++17)
(C++17)
(C++17)
C library
 
Constrained algorithms
Non-modifying sequence operations
Modifying sequence operations
Partitioning operations
Sorting operations
Binary search operations
Set operations (on sorted ranges)
Heap operations
Minimum/maximum operations
Permutations
Operations on uninitialized storage
Return types
 
Defined in header <algorithm>
Call signature
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 unique_copy_result<I, O>

          unique_copy( I first, S last, O result, C comp = {}, Proj proj = {} );
(1) (since C++20)
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 unique_copy_result<ranges::borrowed_iterator_t<R>, O>

          unique_copy( R&& r, O result, C comp = {}, Proj proj = {} );
(2) (since C++20)
Helper types
template<class I, class O>
  using unique_copy_result = ranges::in_out_result<I, O>;
(3) (since C++20)
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:

In practice, they may be implemented as function objects, or with special compiler extensions.

Contents

[edit] 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

[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> 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{};

[edit] Example

#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

[edit] See also

removes consecutive duplicate elements in a range
(niebloid) [edit]
copies a range of elements to a new location
(niebloid) [edit]
finds the first two adjacent items that are equal (or satisfy a given predicate)
(niebloid) [edit]
creates a copy of some range of elements that contains no consecutive duplicates
(function template) [edit]