C++ Codes
C++ > Visual C++ 5.0 Standard C++ Library sample source codes

Unique - Replace all consecutive matching occurences of a value in the range

Unique - Replace all consecutive matching occurences of a value in the range


unique
	
 
Header
<algorithm>

template<class ForwardIterator>
ForwardIterator unique(ForwardIterator first, ForwardIterator last)

Replace all consecutive matching occurences of a value in the range [first, last) by a single instance of that value. Returns an iterator positioned immediately after the last element of the new sequence.

The non-predicate version uses operator== for comparison.

template<class ForwardIterator, class BinaryPredicate>
ForwardIterator unique(ForwardIterator first, ForwardIterator last, BinaryPredicate pr)

Replace all consecutive matching occurences of a value in the range [first, last) by a single instance of that value. Returns an iterator positioned immediately after the last element of the new sequence.

The predicate version uses predicate function pr for comparison.

NOTE: The size of the container is not altered. If n elements were removed the last n elements of the sequence will be undefined.


Sample

#pragma warning(disable : 4786)

#include <algorithm>
#include <iostream>
#include <functional>
#include <vector>

int main()
{
	std::vector<int> vi1(10), vi2(10) ;
	std::vector<int>::iterator last ;

	vi1[0] = 1 ;
	vi1[1] = 1 ;
	vi1[2] = 2 ;
	vi1[3] = 2 ;
	vi1[4] = 3 ;
	vi1[5] = 3 ;
	vi1[6] = 4 ;
	vi1[7] = 4 ;
	vi1[8] = 5 ;
	vi1[9] = 5 ;
	
	std::transform(vi1.begin(), vi1.end(), vi2.begin(), std::negate<int>() ) ;

	std::ostream_iterator<int> intOstreamIt(std::cout, ", ") ;
	
	
	std::cout << "using non-predicate version" << std::endl ;
	std::cout << "\n\nvi1 before unique = " ;
	std::copy(vi1.begin(), vi1.end(), intOstreamIt) ;
	std::cout << std::endl ;

	//remove all duplicates from vi1
	//using non-predicate version
	last = std::unique(vi1.begin(), vi1.end()) ;

	std::cout << "\n\nvi1 after unique = " ;
	std::copy(vi1.begin(), last, intOstreamIt) ;
	std::cout << std::endl ;

	std::cout << "\n\nusing predicate version" << std::endl ;
	std::cout << "\n\nvi2 before unique = " ;
	std::copy(vi2.begin(), vi2.end(), intOstreamIt) ;
	std::cout << std::endl ;

	//remove all duplicates from vi2
	//using predicate version
	last = std::unique(vi2.begin(), vi2.end(), std::equal_to<int>()) ;

	std::cout << "\n\nvi2 after unique = " ;
	std::copy(vi2.begin(), last, intOstreamIt) ;
	std::cout << std::endl ;

	return 0 ;
}

Program output

using non-predicate version


vi1 before unique = 1, 1, 2, 2, 3, 3, 4, 4, 5, 5,


vi1 after unique = 1, 2, 3, 4, 5,


using predicate version


vi2 before unique = -1, -1, -2, -2, -3, -3, -4, -4, -5, -5,


vi2 after unique = -1, -2, -3, -4, -5,