
Category: algorithms  Component type: function 
template <class InputIterator, class OutputIterator> OutputIterator unique_copy(InputIterator first, InputIterator last, OutputIterator result); template <class InputIterator, class OutputIterator, class BinaryPredicate> OutputIterator unique_copy(InputIterator first, InputIterator last, OutputIterator result, BinaryPredicate binary_pred);
The reason there are two different versions of unique_copy is that there are two different definitions of what it means for a consecutive group of elements to be duplicates. In the first version, the test is simple equality: the elements in a range [f, l) are duplicates if, for every iterator i in the range, either i == f or else *i == *(i1). In the second, the test is an arbitrary Binary Predicate binary_pred: the elements in [f, l) are duplicates if, for every iterator i in the range, either i == f or else binary_pred(*i, *(i1)) is true. [1]
const int A[] = {2, 7, 7, 7, 1, 1, 8, 8, 8, 2, 8, 8}; unique_copy(A, A + sizeof(A) / sizeof(int), ostream_iterator<int>(cout, " ")); // The output is "2 7 1 8 2 8".
[1] Strictly speaking, the first version of unique_copy is redundant: you can achieve the same functionality by using an object of class equal_to as the Binary Predicate argument. The first version is provided strictly for the sake of convenience: testing for equality is an important special case.
[2] BinaryPredicate is not required to be an equivalence relation. You should be cautious, though, about using unique_copy with a Binary Predicate that is not an equivalence relation: you could easily get unexpected results.
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