std::unique

From Cppreference

Jump to: navigation, search
Defined in header <algorithm>

template< class ForwardIterator >
ForwardIterator unique( ForwardIterator first, ForwardIterator last );
(1)
template< class ForwardIterator, class BinaryPredicate >
ForwardIterator unique( ForwardIterator first, ForwardIterator last, BinaryPredicate p );
(2)

Removes all consecutive duplicate elements from the range [first, last). Removing is done by shifting the range when needed in such a way that elements to be erased are overwritten. Only the first element in each group of equal elements is left. The elements between the old and the new end or the range are left intact. The first version uses operator== to compare the elements, the second version uses the given binary predicate p.

Contents

[edit] Parameters

first, last - the range of elements to process
p - binary predicate which returns ​true if the elements should be treated as equal.

The signature of the predicate function should be equivalent to the following:

bool pred(const Type1 &a, const Type2 &b);

The signature does not need to have const &, but the function must not modify the objects passed to it.
The types Type1 and Type2 must be such that an object of type ForwardIterator can be dereferenced and then implicitly converted to both of them.

[edit] Return value

forward iterator to the new end of the range

[edit] Equivalent function

[edit] Example

The following code removes all consecutive equivalent elements from a vector of integers.

#include <iostream>
#include <algorithm>
#include <vector>
 
int main() 
{
    std::vector<int> v{1, 2, 2, 2, 3, 3, 2, 2, 1};
    std::vector<int>::iterator last;
 
    last = std::unique(v.begin(), v.end()); // 1 2 3 2 1 3 2 2 1
                                            //           ^
    for (std::vector<int>::iterator it = v.begin(); it != last; ++it) {
        std::cout << *it << " ";
    }
    std::cout << "\n";
}

Output:

1 2 3 2 1

[edit] Complexity

linear in the distance between first and last

[edit] See also

adjacent_find
finds two identical (or some other relationship) items adjacent to each other
(function template)
unique_copy
creates a copy of some range of elements that contains no consecutive duplicates
(function template)