std::ranges::unique_copy, std::ranges::unique_copy_result - cppreference.com (original) (raw)
- 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).
- 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 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 ||
(std::input_iterator && std::same_as<std::iter_value_t,
std::iter_value_t>) || 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 value = *first;
*result = value;
++result;
while (!(++first == last))
{
auto&& value2 = *first;
if ((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,
Proj>> C = ranges::equal_to>
requires std::indirectly_copyable<ranges::iterator_t, O> &&
(std::forward_iterator<ranges::iterator_t> ||
(std::input_iterator && std::same_as<ranges::range_value_t,
std::iter_value_t>) ||
std::indirectly_copyable_storable<ranges::iterator_t, O>)
constexpr ranges::unique_copy_result<ranges::borrowed_iterator_t, 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 #include #include #include #include #include #include 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 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(algorithm function object)[edit] | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | copies a range of elements to a new location(algorithm function object)[edit] | | | finds the first two adjacent items that are equal (or satisfy a given predicate)(algorithm function object)[edit] | | | creates a copy of some range of elements that contains no consecutive duplicates (function template) [edit] |