.. Algorithms/Transformation Algorithms//unique |80

unique

Synopsis

.. parsed-literal::

template<
      typename Seq
    , typename Pred
    , typename In = |unspecified|
    >
struct unique
{
    typedef |unspecified| type;
};

Description

Returns a sequence of the initial elements of every subrange of the original sequence Seq whose elements are all the same.

|transformation algorithm disclaimer|

Header

.. parsed-literal::

#include <boost/mpl/unique.hpp>

Model of

|Reversible Algorithm|

Parameters

+---------------+-----------------------------------+-------------------------------+ | Parameter | Requirement | Description | +===============+===================================+===============================+ | Sequence | |Forward Sequence| | An original sequence. | +---------------+-----------------------------------+-------------------------------+ | Pred | Binary |Lambda Expression| | An equivalence relation. | +---------------+-----------------------------------+-------------------------------+ | In | |Inserter| | An inserter. | +---------------+-----------------------------------+-------------------------------+

Expression semantics

|Semantics disclaimer...| |Reversible Algorithm|.

For any |Forward Sequence| s, a binary |Lambda Expression| pred, and an |Inserter| in:

.. parsed-literal::

typedef unique<s,pred,in>::type r; 

:Return type: A type.

:Semantics: If size<s>::value <= 1, then equivalent to

.. parsed-literal::

    typedef copy<s,in>::type r;

otherwise equivalent to

.. parsed-literal::

    typedef lambda<pred>::type p;
    typedef lambda<in::operation>::type in_op;
    typedef apply_wrap\ ``2``\<
          in_op
        , in::state
        , front<types>::type 
        >::type in_state;

    typedef fold<
          s
        , pair< in_state, front<s>::type >
        , eval_if< 
              apply_wrap\ ``2``\<p, second<_1>, _2>
            , identity< first<_1> >
            , apply_wrap\ ``2``\<in_op, first<_1>, _2>
            >
        >::type::first r;

Complexity

Linear. Performs exactly size<s>::value - 1 applications of pred, and at most size<s>::value insertions.

Example

.. parsed-literal::

typedef vector<int,float,float,char,int,int,int,double> types;
typedef vector<int,float,char,int,double> expected;
typedef unique< types, is_same<_1,_2> >::type result;

BOOST_MPL_ASSERT(( equal< result,expected > ));

See also

|Transformation Algorithms|, |Reversible Algorithm|, |reverse_unique|, |remove|, |copy_if|, |replace_if|

.. copyright:: Copyright 2001-2009 Aleksey Gurtovoy and David Abrahams Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)