std::partial_sum

 

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Algorithm library

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Non-modifying sequence operations
all_of any_of none_of (C++11) (C++11) (C++11) for_each count count_if mismatch equal	find find_if find_if_not (C++11) find_end find_first_of adjacent_find search search_n
Modifying sequence operations
copy copy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) fill fill_n transform generate generate_n remove remove_if remove_copy remove_copy_if	replace replace_if replace_copy replace_copy_if swap swap_ranges iter_swap reverse reverse_copy rotate rotate_copy random_shuffle shuffle   (C++11) unique unique_copy
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is_partitioned (C++11) partition partition_copy (C++11)	stable_partition partition_point (C++11)
Sorting operations (on sorted ranges)
is_sorted (C++11) is_sorted_until (C++11) sort	partial_sort partial_sort_copy stable_sort nth_element
Binary search operations (on sorted ranges)
lower_bound upper_bound	binary_search equal_range
Set operations (on sorted ranges)
merge inplace_merge includes	set_difference set_intersection set_symmetric_difference set_union
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is_heap is_heap_until (C++11) make_heap	push_heap pop_heap sort_heap
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max max_element min min_element minmax (C++11) minmax_element (C++11)	lexicographical_compare is_permutation (C++11) next_permutation prev_permutation
Numeric operations
iota (C++11) accumulate inner_product	adjacent_difference partial_sum
C library
qsort	bsearch

 

Defined in header <numeric>
template< class InputIterator, class OutputIterator > OutputIterator partial_sum( InputIterator first, InputIterator last, OutputIterator d_first );	(1)
template< class InputIterator, class OutputIterator, class BinaryOperation > OutputIterator partial_sum( InputIterator first, InputIterator last, OutputIterator 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);
...

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: Ret fun(const Type1 &a, const Type2 &b); The signature does not need to have const &. The type  Type1 must be such that an object of type iterator_traits<InputIterator>::value_type can be implicitly converted to  Type1. The type  Type2 must be such that an object of type InputIterator can be dereferenced and then implicitly converted to  Type2. The type  Ret must be such that an object of type iterator_traits<InputIterator>::value_type can be assigned a value of type  Ret. ​

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 InputIterator, class OutputIterator> OutputIterator partial_sum(InputIterator first, InputIterator last, OutputIterator d_first) { return std::partial_sum(first, last, d_first, std::plus<InputIterator, InputIterator>()); }
Second version
template<class InputIterator, class OutputIterator, class BinaryOperator> OutputIterator partial_sum(InputIterator first, InputIterator last, OutputIterator d_first, BinaryOperation op) { if (first == last) return d_first;   typename std::iterator_traits<InputIterator>::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};
 
    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

adjacent_difference	computes the differences between adjacent elements in a range (function template)
accumulate	sums up a range of elements (function template)