## unique, unique_copy

    Algorithm

- Summary
- Data Type and Member Function Indexes
- Synopsis
- Description
- Complexity
- Example
- Warnings

### Summary

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

### Data Type and Member Function Indexes
(exclusive of constructors and destructors)

None

### Synopsis

    #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);

### Description

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 that tests for equality and a second that tests adjacent elements against a binary predicate. 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.

### Complexity

For unique_copy, it is exactly `(last - first) - 1` applications of the corresponding predicate are performed.

### Example

    //
    // unique.cpp
    //
    #include <algorithm>
    #include <vector>
    #include <iostream>
    using namespace std;
    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+0, 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,char>(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,char>(cout," "));
    return 0;
    }

Program 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

### Warnings

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

`vector<int, allocator<int> >`

instead of:

`vector<int>`

If your compiler does not support namespaces, then you do not need the using declaration for `std`.

Copyright (c) 1998, Rogue Wave Software, Inc.
Send mail to report errors or comment on the documentation.
OEM Release, June 1998