STL-------------partial_sum

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template <class InputIterator, class OutputIterator>
   OutputIterator partial_sum ( InputIterator first, InputIterator last,
                                OutputIterator result );

template <class InputIterator, class OutputIterator, class BinaryOperation>
   OutputIterator partial_sum ( InputIterator first, InputIterator last,
                                OutputIterator result, BinaryOperation binary_op );

Compute partial sums of range

Assigns to every element in the range starting at result the partial sum of the corresponding elements in the range [first,last).

If x represents an element in [first,last) and y represents an element in result, the ys can be calculated as:

y ₀ = x ₀
y ₁ = x ₀ + x ₁
y ₂ = x ₀ + x ₁ + x ₂
y ₃ = x ₀ + x ₁ + x ₂ + x ₃
y ₄ = x ₀ + x ₁ + x ₂ + x ₃ + x ₄
... ... ...

The default operation is to add the elements up, but a different operation can be specified as binary_op instead.

The behavior of this function template is equivalent to:

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template <class InputIterator, class OutputIterator> OutputIterator partial_sum ( InputIterator first, InputIterator last, OutputIterator result ) { iterator_traits<InputIterator>::value_type val; *result++ = val = *first++; while (first!=last) *result++ = val = val + *first++; // or: *result++ = val = binary_op(val,*first++) for binary_op version return result; }

Parameters

first, last

Input iterators to the initial and final positions in a sequence. The range used is [first,last), which contains all the elements between first and last, including the element pointed by first but not the element pointed by last.

result

Output iterator to the initial position in the destination sequence where the partial sums are stored. The range starts at result and shall have a size large enough to contain as many elements as the range above ( [first,last)).

binary_op

Binary operation taking as arguments two elements of the type pointed by the InputIterator, and returning the result of the replacement for the sum operation. This can either be a pointer to a function or an object whose class overloads operator().

Return value

An iterator pointing to past the last element of the destination sequence where resulting elements have been stored.

Example

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// partial_sum example #include <iostream> #include <functional> #include <numeric> using namespace std; int myop (int x, int y) {return x+y+1;} int main () { int val[] = {1,2,3,4,5}; int result[5]; partial_sum (val, val+5, result); cout << "using default partial_sum: "; for (int i=0; i<5; i++) cout << result[i] << ' '; cout << endl; partial_sum (val, val+5, result, multiplies<int>()); cout << "using functional operation multiplies: "; for (int i=0; i<5; i++) cout << result[i] << ' '; cout << endl; partial_sum (val, val+5, result, myop); cout << "using custom function: "; for (int i=0; i<5; i++) cout << result[i] << ' '; cout << endl; return 0; }

 

 

#include <iostream>
#include <functional>
#include <numeric>
using namespace std;

int myop (int x, int y) {return x+y+1;}

int main () {
  int val[] = {1,2,3,4,5};
  int result[5];

  partial_sum (val, val+5, result);
  cout << "using default partial_sum: ";
  for (int i=0; i<5; i++) cout << result[i] << ' ';
  cout << endl;

  partial_sum (val, val+5, result, multiplies<int>());
  cout << "using functional operation multiplies: ";
  for (int i=0; i<5; i++) cout << result[i] << ' ';
  cout << endl;

  partial_sum (val, val+5, result, myop);
  cout << "using custom function: ";
  for (int i=0; i<5; i++) cout << result[i] << ' ';
  cout << endl;
  return 0;
}

 

Output:

using default partial_sum: 1 3 6 10 15 using functional operation multiplies: 1 2 6 24 120 using custom function: 1 4 8 13 19