Standard C++ LibraryCopyright 1996, Rogue Wave Software, Inc.

NAME

  partial_sort  - Templated algorithm for sorting collections of entities.

SYNOPSIS

  #include <algorithm>

  template <class RandomAccessIterator>
  void partial_sort (RandomAccessIterator first,
                     RandomAccessIterator middle,
                     RandomAccessIterator last);

  template <class RandomAccessIterator, class Compare>
  void partial_sort (RandomAccessIterator first,
                     RandomAccessIterator middle,
                     RandomAccessIterator last, Compare comp);

DESCRIPTION

  The partial_sort algorithm takes the range [first,last) and places the
  first middle - first values into sorted order.  The result is that the
  range [first, middle)is sorted like it would be if the entire range
  [first,last) were sorted.  The remaining elements in the range (those in
  [middle, last)) are not in any defined order.  The first version of the
  algorithm uses less than (operator<) as the comparison operator for the
  sort.  The second version uses the comparison function comp.

COMPLEXITY

  partial_sort does approximately (last  - first) * log(middle-first)
  comparisons.

EXAMPLE

  //
  // partsort.cpp
  //
  #include <vector>
  #include <algorithm>
  #include <iostream.h>

  int main()
   {
    int d1[20] = {17, 3,  5,  -4, 1, 12, -10, -1, 14, 7,
                   -6, 8, 15, -11, 2, -2,  18,  4, -3, 0};
     //
     // Set up a vector.
     //
    vector<int> v1(d1+0, d1+20);
     //
     // Output original vector.
     //
    cout << "For the vector: ";
    copy(v1.begin(), v1.end(),
         ostream_iterator<int,char>(cout," "));
     //
     // Partial sort the first seven elements.
     //
     partial_sort(v1.begin(), v1.begin()+7, v1.end());
     //
     // Output result.
     //
    cout << endl << endl << "A partial_sort of seven elements
                             gives: "
          << endl << "     ";
    copy(v1.begin(), v1.end(),
         ostream_iterator<int,char>(cout," "));
    cout << endl;
     //
     // A vector of ten elements.
     //
    vector<int> v2(10, 0);
     //
     // Sort the last ten elements in v1 into v2.
     //
    partial_sort_copy(v1.begin()+10, v1.end(), v2.begin(),
                      v2.end());
     //
     // Output result.
     //
    cout << endl << "A partial_sort_copy of the last ten elements
                     gives: "
          << endl << "     ";
    copy(v2.begin(), v2.end(),
         ostream_iterator<int,char>(cout," "));
    cout << endl;

    return 0;
   }

  Output :
  For the vector: 17 3 5 -4 1 12 -10 -1 14 7 -6 8 15 -11 2 -2 18 4 -3 0
  A partial_sort of seven elements gives:
       -11 -10 -6 -4 -3 -2 -1 17 14 12 7 8 15 5 3 2 18 4 1 0
  A partial_sort_copy of the last ten elements gives:
      0 1 2 3 4 5 7 8 15 18

WARNING

  If your compiler does not support default template parameters, then you
  need to always provide the Allocator template argument.  For instance, you
  will need to write :

  vector<int, allocator<int> >

  instead of :

  vector<int>

SEE ALSO

  sort, stable_sort, partial_sort_copy

STANDARDS CONFORMANCE

  ANSI X3J16/ISO WG21 Joint C++ Committee



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