27 Algorithms library [algorithms]

27.7 Mutating sequence operations [alg.modifying.operations]

27.7.9 Unique [alg.unique]

template<class ForwardIterator>
  constexpr ForwardIterator unique(ForwardIterator first, ForwardIterator last);
template<class ExecutionPolicy, class ForwardIterator>
  ForwardIterator unique(ExecutionPolicy&& exec,
                         ForwardIterator first, ForwardIterator last);

template<class ForwardIterator, class BinaryPredicate>
  constexpr ForwardIterator unique(ForwardIterator first, ForwardIterator last,
                                   BinaryPredicate pred);
template<class ExecutionPolicy, class ForwardIterator, class BinaryPredicate>
  ForwardIterator unique(ExecutionPolicy&& exec,
                         ForwardIterator first, ForwardIterator last,
                         BinaryPredicate pred);

template<permutable I, sentinel_for<I> S, class Proj = identity,
         indirect_equivalence_relation<projected<I, Proj>> C = ranges::equal_to>
  constexpr subrange<I> ranges::unique(I first, S last, C comp = {}, Proj proj = {});
template<forward_range R, class Proj = identity,
         indirect_equivalence_relation<projected<iterator_t<R>, Proj>> C = ranges::equal_to>
  requires permutable<iterator_t<R>>
  constexpr borrowed_subrange_t<R>
    ranges::unique(R&& r, C comp = {}, Proj proj = {});

Let pred be equal_to{} for the overloads with no parameter pred, and let E be

(1.1)
bool(pred(*(i - 1), *i)) for the overloads in namespace std;
(1.2)
bool(invoke(comp, invoke(proj, *(i - 1)), invoke(proj, *i))) for the overloads in namespace ranges.

Preconditions: For the overloads in namespace std, pred is an equivalence relation and the type of *first meets the Cpp17MoveAssignable requirements (Table 33).

Effects: For a nonempty range, eliminates all but the first element from every consecutive group of equivalent elements referred to by the iterator i in the range [first + 1, last) for which E is true.

Returns: Let j be the end of the resulting range.

Returns:

(4.1)
j for the overloads in namespace std.
(4.2)
{j, last} for the overloads in namespace ranges.

Complexity: For nonempty ranges, exactly (last - first) - 1 applications of the corresponding predicate and no more than twice as many applications of any projection.

🔗

template<class InputIterator, class OutputIterator>
  constexpr OutputIterator
    unique_copy(InputIterator first, InputIterator last,
                OutputIterator result);
template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2>
  ForwardIterator2
    unique_copy(ExecutionPolicy&& exec,
                ForwardIterator1 first, ForwardIterator1 last,
                ForwardIterator2 result);

template<class InputIterator, class OutputIterator,
         class BinaryPredicate>
  constexpr OutputIterator
    unique_copy(InputIterator first, InputIterator last,
                OutputIterator result, BinaryPredicate pred);
template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2,
         class BinaryPredicate>
  ForwardIterator2
    unique_copy(ExecutionPolicy&& exec,
                ForwardIterator1 first, ForwardIterator1 last,
                ForwardIterator2 result, BinaryPredicate pred);

template<input_iterator I, sentinel_for<I> S, weakly_incrementable O, class Proj = identity,
         indirect_equivalence_relation<projected<I, Proj>> C = ranges::equal_to>
  requires indirectly_copyable<I, O> &&
           (forward_iterator<I> ||
            (input_iterator<O> && same_as<iter_value_t<I>, iter_value_t<O>>) ||
            indirectly_copyable_storable<I, O>)
  constexpr ranges::unique_copy_result<I, O>
    ranges::unique_copy(I first, S last, O result, C comp = {}, Proj proj = {});
template<input_range R, weakly_incrementable O, class Proj = identity,
         indirect_equivalence_relation<projected<iterator_t<R>, Proj>> C = ranges::equal_to>
  requires indirectly_copyable<iterator_t<R>, O> &&
           (forward_iterator<iterator_t<R>> ||
            (input_iterator<O> && same_as<range_value_t<R>, iter_value_t<O>>) ||
            indirectly_copyable_storable<iterator_t<R>, O>)
  constexpr ranges::unique_copy_result<borrowed_iterator_t<R>, O>
    ranges::unique_copy(R&& r, O result, C comp = {}, Proj proj = {});

Let pred be equal_to{} for the overloads in namespace std with no parameter pred, and let E be

(6.1)
bool(pred(*i, *(i - 1))) for the overloads in namespace std;
(6.2)
bool(invoke(comp, invoke(proj, *i), invoke(proj, *(i - 1)))) for the overloads in namespace ranges.

Mandates: *first is writable ([iterator.requirements.general]) to result.

Preconditions:

(8.1)
The ranges [first, last) and [result, result+(last-first)) do not overlap.
(8.2)
For the overloads in namespace std:
- (8.2.1)
  The comparison function is an equivalence relation.
- (8.2.2)
  For the overloads with no ExecutionPolicy, let T be the value type of InputIterator.
  
  If InputIterator models forward_iterator ([iterator.concept.forward]), then there are no additional requirements for T.
  
  Otherwise, if OutputIterator meets the Cpp17ForwardIterator requirements and its value type is the same as T, then T meets the Cpp17CopyAssignable (Table 34) requirements.
  
  Otherwise, T meets both the Cpp17CopyConstructible (Table 32) and Cpp17CopyAssignable requirements.
  
  [Note 1:
  For the overloads with an ExecutionPolicy, there might be a performance cost if the value type of ForwardIterator1 does not meet both the Cpp17CopyConstructible and Cpp17CopyAssignable requirements.
  — end note]

Effects: Copies only the first element from every consecutive group of equal elements referred to by the iterator i in the range [first, last) for which E holds.

Returns:

(10.1)
result + N for the overloads in namespace std.
(10.2)
{last, result + N} for the overloads in namespace ranges.

Complexity: Exactly last - first - 1 applications of the corresponding predicate and no more than twice as many applications of any projection.