| Defined in header <numeric> | ||
|---|---|---|
template< class InputIt, class OutputIt > OutputIt partial_sum( InputIt first, InputIt last, OutputIt d_first ); | (1) | |
template< class InputIt, class OutputIt, class BinaryOperation >
OutputIt partial_sum( InputIt first, InputIt last, OutputIt d_first,
BinaryOperation op ); | (2) |
Computes the partial sums of the elements in the subranges of the range [first, last) and writes them to the range beginning at d_first. The first version uses operator+ to sum up the elements, the second version uses the given binary function op.
Equivalent operation:
*(d_first) = *first; *(d_first+1) = *first + *(first+1); *(d_first+2) = *first + *(first+1) + *(first+2); *(d_first+3) = *first + *(first+1) + *(first+2) + *(first+3); ...
|
| (until C++11) |
|
| (since C++11) |
Parameters
| first, last | - | the range of elements to sum |
| d_first | - | the beginning of the destination range |
| op | - | binary operation function object that will be applied. The signature of the function should be equivalent to the following:
The signature does not need to have |
| Type requirements | ||
- InputIt must meet the requirements of InputIterator. | ||
- OutputIt must meet the requirements of OutputIterator. | ||
Return value
Iterator to the element past the last element written.
Complexity
Exactly (last - first) - 1 applications of the binary operation.
Possible implementation
| First version |
|---|
template<class InputIt, class OutputIt>
OutputIt partial_sum(InputIt first, InputIt last,
OutputIt d_first)
{
if (first == last) return d_first;
typename std::iterator_traits<InputIt>::value_type sum = *first;
*d_first = sum;
while (++first != last) {
sum = sum + *first;
*++d_first = sum;
}
return ++d_first;
// or, since C++14:
// return std::partial_sum(first, last, d_first, std::plus<>());
} |
| Second version |
template<class InputIt, class OutputIt, class BinaryOperation>
OutputIt partial_sum(InputIt first, InputIt last,
OutputIt d_first, BinaryOperation op)
{
if (first == last) return d_first;
typename std::iterator_traits<InputIt>::value_type sum = *first;
*d_first = sum;
while (++first != last) {
sum = op(sum, *first);
*++d_first = sum;
}
return ++d_first;
} |
Example
#include <numeric>
#include <vector>
#include <iostream>
#include <iterator>
#include <functional>
int main()
{
std::vector<int> v = {2, 2, 2, 2, 2, 2, 2, 2, 2, 2}; // or std::vector<int>v(10, 2);
std::cout << "The first 10 even numbers are: ";
std::partial_sum(v.begin(), v.end(),
std::ostream_iterator<int>(std::cout, " "));
std::cout << '\n';
std::partial_sum(v.begin(), v.end(), v.begin(), std::multiplies<int>());
std::cout << "The first 10 powers of 2 are: ";
for (auto n : v) {
std::cout << n << " ";
}
std::cout << '\n';
}Output:
The first 10 even numbers are: 2 4 6 8 10 12 14 16 18 20 The first 10 powers of 2 are: 2 4 8 16 32 64 128 256 512 1024
See also
| computes the differences between adjacent elements in a range (function template) | |
| sums up a range of elements (function template) | |
| (parallelism TS) | similar to std::partial_sum, includes the ith input element in the ith sum (function template) |
| (parallelism TS) | similar to std::partial_sum, excludes the ith input element from the ith sum (function template) |
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