C++ Numeric::partial_sum() function

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The C++ std::numeric::partial_sum() function is used to return the partial sums of the range of elements. It processes a sequence of numbers and produces a new sequence where each element is the cumulative sum of the elements up to that point. It also accepts a binary operation form custom accumulation.

Syntax

Following is the syntax for std::numeric::partial_sum() function.

	
OutputIterator partial_sum (InputIterator first, InputIterator last, OutputIterator result);
or
OutputIterator partial_sum (InputIterator first, InputIterator last, OutputIterator result, BinaryOperation binary_op);

Parameters

• first, last − It indicates the iterators to the initial and final positions in a sequence.
• result − It is an output iterator to the initial position in the destination sequence where the partial sum is stored.
• binary_op − It is binary operation.

Return Value

It returns an iterator pointing to past the last element of the destination sequence where resulting elements have been stored, or result if [first,last) is an empty range.

Exceptions

It throws if any of the operations on the elements or iterators throws.

Data races

The elements in the range [first1,last1) are accessed.

Example 1

In the following example, we are going to consider the basic usage of the partial_sum() function.

#include <iostream>
#include <numeric>
#include <vector>
int main() {
   std::vector < int > x = {2,4,6};
   std::vector < int > y(3);
   std::partial_sum(x.begin(), x.end(), y.begin());
   for (int x: y)
      std::cout << x << " ";
   return 0;
}

Output

Output of the above code is as follows −

2 6 12

Example 2

Consider the following example, where we are going to use perform the simple addition with partial_sum().

#include <iostream>
#include <numeric>
#include <vector>
int main() {
   std::vector < int > x = {1,3,5};
   std::vector < int > y(x.size());
   std::partial_sum(x.begin(), x.end(), y.begin());
   for (int a: y)
      std::cout << a << " ";
   return 0;
}

Output

Following is the output of the above code −

1 4 9

Example 3

Let's look at the following example, where we are going to perform the cumulative subtraction.

#include <iostream>
#include <numeric>
#include <vector>
int main() {
   std::vector < int > a = {2,4,6};
   std::vector < int > b(a.size());
   std::partial_sum(a.begin(), a.end(), b.begin(), std::minus < int > ());
   for (int x: b)
      std::cout << x << " ";
   return 0;
}

Output

If we run the above code it will generate the following output −

2 -2 -8