stable_partition

Artikel
07/29/2015

Classifies elements in a range into two disjoint sets, with those elements satisfying a unary predicate preceding those that fail to satisfy it, preserving the relative order of equivalent elements.

template<class BidirectionalIterator, class Predicate> 
   BidirectionalIterator stable_partition( 
      BidirectionalIterator _First,  
      BidirectionalIterator _Last, 
      Predicate _Pred 
   );

Parameters

_First
A bidirectional iterator addressing the position of the first element in the range to be partitioned.
_Last
A bidirectional iterator addressing the position one past the final element in the range to be partitioned.
_Pred
User-defined predicate function object that defines the condition to be satisfied if an element is to be classified. A predicate takes single argument and returns true or false.

Return Value

A bidirectional iterator addressing the position of the first element in the range to not satisfy the predicate condition.

Remarks

The range referenced must be valid; all pointers must be dereferenceable and within the sequence the last position is reachable from the first by incrementation.

Elements a and b are equivalent, but not necessarily equal, if both Pr (a, b) is false and Pr (b, a) if false, where Pr is the parameter-specified predicate. The stable_ partition algorithm is stable and guarantees that the relative ordering of equivalent elements will be preserved. The algorithm partition does not necessarily preserve this original ordering.

Example

// alg_stable_partition.cpp
// compile with: /EHsc
#include <vector>
#include <algorithm>
#include <iostream>

bool greater5 ( int value ) {
   return value >5;
}

int main( ) {
   using namespace std;
   vector <int> v1, v2;
   vector <int>::iterator Iter1, Iter2, result;

   int i;
   for ( i = 0 ; i <= 10 ; i++ )
      v1.push_back( i );

   int ii;
   for ( ii = 0 ; ii <= 4 ; ii++ )
      v1.push_back( 5 );

   random_shuffle(v1.begin( ), v1.end( ) );

   cout << "Vector v1 is ( " ;
   for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ )
      cout << *Iter1 << " ";
   cout << ")." << endl;

   // Partition the range with predicate greater10
   result = stable_partition (v1.begin( ), v1.end( ), greater5 );
   cout << "The partitioned set of elements in v1 is:\n ( " ;
   for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ )
      cout << *Iter1 << " ";
   cout << ")." << endl;

   cout << "The first element in v1 to fail to satisfy the"
        << "\n predicate greater5 is: " << *result << "." << endl;
}

Sample Output

Vector v1 is ( 5 1 9 2 0 5 7 3 4 5 8 5 5 5 10 6 ).
The partitioned set of elements in v1 is:
 ( 9 7 8 10 6 5 1 2 0 5 3 4 5 5 5 5 ).
The first element in v1 to fail to satisfy the
 predicate greater5 is: 5.

Requirements

Header: <algorithm>

Namespace: std

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