unique, unique_copy

     Algorithm

Removes consecutive duplicates from a range of values and places the resulting unique values into the result.

Contents

• Synopsis
• Description
• Complexity
• Example
• Warning

#include <algorithm>

template <class ForwardIterator>
ForwardIterator unique (ForwardIterator first,
                        ForwardIterator last);
template <class ForwardIterator, class BinaryPredicate>
ForwardIterator unique (ForwardIterator first,
                        ForwardIterator last,
                        BinaryPredicate binary_pred);
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 unique algorithm moves through a sequence and eliminates all but the first element from every consecutive group of equal elements. There are two versions of the algorithm, one tests for equality, and the other tests whether a binary predicate applied to adjacent elements is true. An element is unique if it does not meet the corresponding condition listed here:

  *i  ==  *(i  -  1)  

or

binary_pred(*i, *(i - 1)) == true. 

If an element is unique, it is copied to the front of the sequence, overwriting the existing elements. Once all unique elements have been identified. The remainder of the sequence is left unchanged, and unique returns the end of the resulting range.

The unique_copy algorithm copies the first element from every consecutive group of equal elements, to an OutputIterator. The unique_copy algorithm, also has two versions--one that tests for equality and a second that tests adjacent elements against a binary predicate.

unique_copy returns the end of the resulting range.

Exactly (last - first) - 1 applications of the corresponding predicate are performed.

//
// unique.cpp
//
 #include <algorithm>
 #include <vector>
 #include <iostream.h>
 int main()
 {
   //Initialize two vectors
   int a1[20] = {4, 5, 5, 9, -1, -1, -1, 3, 7, 5, 
                 5, 5, 6, 7, 7, 7, 4, 2, 1, 1};
   vector<int> v(a1, a1+20), result;

   //Create an insert_iterator for results
   insert_iterator<vector<int> > ins(result, 
                                  result.begin());

   //Demonstrate includes
   cout << "The vector: " << endl << "    ";
   copy(v.begin(),v.end(),ostream_iterator<int>(cout," "));

   //Find the unique elements
   unique_copy(v.begin(), v.end(), ins);

   //Display the results
   cout << endl << endl
        << "Has the following unique elements:"
        << endl << "     ";
   copy(result.begin(),result.end(),
        ostream_iterator<int>(cout," "));

   return 0;
}

Output :
The vector:
    4 5 5 9 -1 -1 -1 3 7 5 5 5 6 7 7 7 4 2 1 1
Has the following unique elements:
     4 5 9 -1 3 7 5 6 7 4 2 1

If your compiler does not support default template parameters, then you need to always supply the Allocator template argument. For instance, you will need to write :

vector<int, allocator>

instead of:

vector<int>