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partial_sum
function template
<numeric>
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:
y0 = x0
y1 = x0 + x1
y2 = x0 + x1 + x2
y3 = x0 + x1 + x2 + x3
y4 = x0 + x1 + x2 + x3 + x4
... ... ...
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;
}
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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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// parcial_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;
}
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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
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See also
| accumulate | Accumulate values in range (function template) |
| inner_product | Compute cumulative inner product of range (function template) |
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