NAME¶

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

Synopsis¶

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> || (since
(std::input_iterator<O> && (1) C++20)
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 = {}
);
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> && (since
(std::forward_iterator<ranges::iterator_t<R>> || (2) C++20)
(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 = {} );

Helper types¶

template< class I, class O > (3) (since
using unique_copy_result = ranges::in_out_result<I, O>; 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:

* 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> ||
(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));
} };

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¶

ranges::unique removes consecutive duplicate elements in a range
(C++20) (niebloid)
ranges::copy
ranges::copy_if copies a range of elements to a new location
(C++20) (niebloid)
(C++20)
ranges::adjacent_find finds the first two adjacent items that are equal (or satisfy
(C++20) a given predicate)
(niebloid)
creates a copy of some range of elements that contains no
unique_copy consecutive duplicates
(function template)