Task: Forward difference


C++: #include <vector>
#include <iterator>
#include <algorithm>









template<typename InputIterator, typename OutputIterator>
 OutputIterator forward_difference(InputIterator first, InputIterator last,
                                   OutputIterator dest)
{
  
  if (first == last)
    return dest;

  typedef typename std::iterator_traits<InputIterator>::value_type value_type;

  value_type temp = *first++;
  while (first != last)
  {
    value_type temp2 = *first++;
    *dest++ = temp2 - temp;
    temp = temp2;
  }

  return dest;
}











template<typename InputIterator, typename OutputIterator>
 OutputIterator nth_forward_difference(int order,
                                       InputIterator first, InputIterator last,
                                       OutputIterator dest)
{
  
  if (order == 0)
    return std::copy(first, last, dest);

  
  if (order == 1)
    return forward_difference(first, last, dest);

  
  typedef typename std::iterator_traits<InputIterator>::value_type value_type;
  std::vector<value_type> temp_storage;

  
  forward_difference(first, last, std::back_inserter(temp_storage));

  
  typename std::vector<value_type>::iterator begin = temp_storage.begin(),
                                             end = temp_storage.end();
  for (int i = 1; i < order-1; ++i)
    end = forward_difference(begin, end, begin);

  
  return forward_difference(begin, end, dest);
}


#include <iostream>

int main()
{
  double array[10] = { 90.0, 47.0, 58.0, 29.0, 22.0, 32.0, 55.0, 5.0, 55.0, 73.0 };

  
  std::vector<double> dest;
  nth_forward_difference(1, array, array+10, std::back_inserter(dest));

  
  std::copy(dest.begin(), dest.end(), std::ostream_iterator<double>(std::cout, " "));
  std::cout << std::endl;

  
  nth_forward_difference(2, array, array+10, std::ostream_iterator<double>(std::cout, " "));
  std::cout << std::endl;

  nth_forward_difference(9, array, array+10, std::ostream_iterator<double>(std::cout, " "));
  std::cout << std::endl;

  nth_forward_difference(10, array, array+10, std::ostream_iterator<double>(std::cout, " "));
  std::cout << std::endl;

  nth_forward_difference(0, array, array+10, std::ostream_iterator<double>(std::cout, " "));
  std::cout << std::endl;

  
  
  double* end = nth_forward_difference(3, array, array+10, array);

  for (double* p = array; p < end; ++p)
    std::cout << *p << " ";
  std::cout << std::endl;

  return 0;
}







VB: Module ForwardDifference

    Sub Main()
        Dim lNum As New List(Of Integer)(New Integer() {90, 47, 58, 29, 22, 32, 55, 5, 55, 73})
        For i As UInteger = 0 To 9
            Console.WriteLine(String.Join(" ", (From n In Difference(i, lNum) Select String.Format("{0,5}", n)).ToArray()))
        Next
        Console.ReadKey()
    End Sub

    Private Function Difference(ByVal Level As UInteger, ByVal Numbers As List(Of Integer)) As List(Of Integer)
        If Level >= Numbers.Count Then Throw New ArgumentOutOfRangeException("Level", "Level must be less than number of items in Numbers")

        For i As Integer = 1 To Level
            Numbers = (From n In Enumerable.Range(0, Numbers.Count - 1) _
                       Select Numbers(n + 1) - Numbers(n)).ToList()
        Next

        Return Numbers
    End Function

End Module