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stable_partition

Same as partition(), but preserves the relative order of matching and nonmatching elements
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Key Facts

Gyroscopic Couple: The rate of change of angular momentum (\tau) = I\omega\Omega (In the limit).
  • I = Moment of Inertia.
  • \omega = Angular velocity
  • \Omega = Angular velocity of precession.


Blaise Pascal (1623-1662) was a French mathematician, physicist, inventor, writer and Catholic philosopher.

Leonhard Euler (1707-1783) was a pioneering Swiss mathematician and physicist.

Definition

The stable_partition() algorithm is defined in the standard header <algorithm> and in the nonstandard backward-compatibility header <algo.h>.

Interface

#include <algorithm>
template < class BidirectionalIterator, class Predicate >
   BidirectionalIterator stable_partition(
      BidirectionalIterator first, 
      BidirectionalIterator last,
      Predicate pred
   );

Parameters:
Parameter Description
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

Description

Stable_partition function does the same thing that partition, except that the relative order between elements is kept. Thus, stable partition uses more computation time than partition.

Return Value

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

Complexity

Performs exactly last - first applications of the predicate and at most (last -first)*log(last - first) swaps if there is insufficient memory or linear number of swaps if sufficient memory is available.
Example:

Example - stable_partition algorithm
Problem
This program illustrates the functionality of stable_partition() algorithm.
Workings
#include <vector>
#include <algorithm>
#include <iostream>
using namespace std;
 
bool greaterthan(int value )
{    return value > 5;    }
 
int main()
{
  vector <int> vec1, vec2;
  vector <int>::iterator Iter1, Iter2, result;
  int i,j;
  for(i = 0; i <= 10; i++)
    vec1.push_back(i);
  for(j = 0; j <= 4; j++)
    vec1.push_back(3);
  random_shuffle(vec1.begin(), vec1.end());
  cout <<"Random shuffle vector vec1 data:\n";
  for (Iter1 = vec1.begin(); Iter1 != vec1.end(); Iter1++)
    cout <<*Iter1<<" ";
  cout <<endl;
  // partition the range with predicate greater than 5...
  result = stable_partition (vec1.begin(), vec1.end(), greaterthan);
  cout <<"\nThe partitioned set of elements in vec1 is:\n";
  for (Iter1 = vec1.begin(); Iter1 != vec1.end(); Iter1++)
    cout <<*Iter1<<" ";
  cout <<endl;
  cout <<"\nThe first element in vec1 fail to satisfy " 
         "the predicate greaterthan is:\n "<<*result<<endl;
 
  return 0;
}
Solution
Output:

Random shuffle vector vec1 data:
3 1 9 2 0 3 7 3 4 3 8 5 3 3 10 6

The partitioned set of elements in vec1 is:
9 7 8 10 6 3 1 2 0 3 3 4 3 5 3 3

The first element in vec1 fail to satisfy the predicate greaterthan is:
3
References

See Also