std::list::unique

 

C++

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Technical Specifications

 

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list::beginlist::cbegin (C++11)

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void unique();	(1)
template< class BinaryPredicate > void unique( BinaryPredicate p );	(2)

Removes all consecutive duplicate elements from the container. Only the first element in each group of equal elements is left. The first version uses operator== to compare the elements, the second version uses the given binary predicate p.

Parameters

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 list<T,Allocator>::const_iterator can be dereferenced and then implicitly converted to both of them. ​

Return value

(none)

Complexity

Linear in the size of the container

Example

Run this code

#include <iostream>
#include <list>
 
int main()
{
  std::list<int> x = {1, 2, 2, 3, 3, 2, 1, 1, 2};
 
  std::cout << "contents before:";
  for (auto val : x)
    std::cout << ' ' << val;
  std::cout << '\n';
 
  x.unique();
  std::cout << "contents after unique():";
  for (auto val : x)
    std::cout << ' ' << val;
  std::cout << '\n';
 
  return 0;
}

Output:

contents before: 1 2 2 3 3 2 1 1 2
contents after unique(): 1 2 3 2 1 2

See also

unique

removes consecutive duplicate elements in a range (function template)