The function-like entities described on this page arealgorithm function objects (informally known asniebloids), that is:

• Explicit template argument lists cannot be specified when calling any of them.
• None of them are visible toargument-dependent lookup.
• When any of them are found bynormal unqualified lookup as the name to the left of the function-call operator,argument-dependent lookup is inhibited.

[edit]Parameters

[edit]Return value

Returns{ret, last}, whereret is a past-the-end iterator for the new end of the range.

[edit]Complexity

For nonempty ranges, exactlyranges::distance(first, last)-1 applications of the corresponding predicatecomp and no more that twice as many applications of any projectionproj.

[edit]Notes

Removing is done by shifting (by means of move assignment) the elements in the range in such a way that the elements that are not to be removed appear in the beginning of the range. Relative order of the elements that remain is preserved and thephysical size of the container is unchanged. Iterators in[ret, last) (if any) are still dereferenceable, but the elements themselves have unspecified values (as perMoveAssignable post-condition).

A call toranges::unique is sometimes followed by a call to a container’serase member function, which erases the unspecified values and reduces thephysical size of the container to match its newlogical size. These two invocations together model theErase–remove idiom.

[edit]Possible implementation

struct unique_fn{template<std::permutable I,std::sentinel_for<I> S,class Proj=std::identity,std::indirect_equivalence_relation<std::projected<I, Proj>>                 C=ranges::equal_to>constexprranges::subrange<I>        operator()(I first, S last, C comp={}, Proj proj={})const{        first=ranges::adjacent_find(first, last, comp, proj);if(first== last)return{first, first};auto i{first};++first;while(++first!= last)if(!std::invoke(comp,std::invoke(proj,*i),std::invoke(proj,*first)))*++i=ranges::iter_move(first);return{++i, first};} template<ranges::forward_range R,class Proj=std::identity,std::indirect_equivalence_relation<std::projected<ranges::iterator_t<R>, Proj>>                 C=ranges::equal_to>    requiresstd::permutable<ranges::iterator_t<R>>constexprranges::borrowed_subrange_t<R>        operator()(R&& r, C comp={}, Proj proj={})const{return(*this)(ranges::begin(r),ranges::end(r),                       std::move(comp), std::move(proj));}}; inlineconstexpr unique_fn unique{};

[edit]Example

#include <algorithm>#include <cmath>#include <complex>#include <iostream>#include <vector> struct id{int i;explicit id(int i): i{i}{}}; void print(id i,constauto& v){std::cout<< i.i<<") ";    std::ranges::for_each(v,[](autoconst& e){std::cout<< e<<' ';});std::cout<<'\n';} int main(){// a vector containing several duplicated elementsstd::vector<int> v{1,2,1,1,3,3,3,4,5,4};     print(id{1}, v); // remove consecutive (adjacent) duplicatesconstauto ret= std::ranges::unique(v);// v now holds {1 2 1 3 4 5 4 x x x}, where 'x' is indeterminate    v.erase(ret.begin(), ret.end());    print(id{2}, v); // sort followed by unique, to remove all duplicates    std::ranges::sort(v);// {1 1 2 3 4 4 5}    print(id{3}, v); constauto[first, last]= std::ranges::unique(v.begin(), v.end());// v now holds {1 2 3 4 5 x x}, where 'x' is indeterminate    v.erase(first, last);    print(id{4}, v); // unique with custom comparison and projectionstd::vector<std::complex<int>> vc{{1,1},{-1,2},{-2,3},{2,4},{-3,5}};    print(id{5}, vc); constauto ret2= std::ranges::unique(vc,// consider two complex nums equal if their real parts are equal by module:[](int x,int y){return std::abs(x)== std::abs(y);},// comp[](std::complex<int> z){return z.real();}// proj);    vc.erase(ret2.begin(), ret2.end());    print(id{6}, vc);}

1) 1 2 1 1 3 3 3 4 5 42) 1 2 1 3 4 5 43) 1 1 2 3 4 4 54) 1 2 3 4 55) (1,1) (-1,2) (-2,3) (2,4) (-3,5)6) (1,1) (-2,3) (-3,5)

[edit]See also

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