# Man Page unique.3

```
Standard C++ Library
Copyright 1998, Rogue Wave Software, Inc.

```

## NAME

```     unique, unique_copy

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

```

## 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 result-
ing range.

The unique_copy algorithm  copies  the  first  element  from
every consecutive group of equal elements to an OutputItera-
tor. 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  applica-
tions 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  parame-
ters,  then you always need to supply the Allocator template
argument. For instance, you need to write:

vector<int, allocator<int> >

vector<int>

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

```