std::adjacent_difference

 

C++

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Algorithm library

Functions
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
Heap operations
is_heap is_heap_until (C++11) make_heap	push_heap pop_heap sort_heap
Minimum/maximum operations
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 adjacent_difference( InputIterator first, InputIterator last,                                     OutputIterator d_first );	(1)
template< class InputIterator, class OutputIterator, class BinaryOperation > OutputIterator adjacent_difference( InputIterator first, InputIterator last,                                     OutputIterator d_first,                                     BinaryOperation op );	(2)

Computes the differences between the second and the first of each adjacent pair of elements of the range [first, last) and writes them to the range beginning at d_first + 1. Unmodified copy of first is written to d_first. The first version uses operator- to calculate the differences, the second version uses the given binary function op.

Equivalent operation:

*(d_first)   = *first;
*(d_first+1) = (*first+1) - *(first);
*(d_first+2) = (*first+2) - *(first+1);
*(d_first+3) = (*first+3) - *(first+2);
...

Parameters

first, last	-	the range of elements
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 types  Type1 and  Type2 must be such that an object of type iterator_traits<InputIterator>::value_type can be implicitly converted to both of them. The type  Ret must be such that an object of type OutputIterator can be dereferenced and 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 adjacent_difference(InputIterator first, InputIterator last, OutputIterator d_first) { if (first == last) return d_first;   typedef typename std::iterator_traits<InputIterator>::value_type value_t; value_t acc = *first; *d_first = acc; while (++first != last) { value_t val = *first; *++d_first = val - acc; acc = std::move(val); } return ++d_first; }
Second version
template<class InputIterator, class T, class BinaryOperation> OutputIterator adjacent_difference(InputIterator first, InputIterator last, OutputIterator d_first, BinaryOperation op) { if (first == last) return d_first;   typedef typename std::iterator_traits<InputIterator>::value_type value_t; value_t acc = *first; *d_first = acc; while (++first != last) { value_t val = *first; *++d_first = op(val, acc); acc = std::move(val); } return ++d_first; }

Example

The following code converts a sequence of even numbers to repetitions of the number 2 and converts a sequence of ones to a sequence of Fibonacci numbers.

​#include <numeric>
#include <vector>
#include <iostream>
#include <functional>
int main()
{
    std::vector<int> v{2, 4, 6, 8, 10, 12, 14, 16, 18, 20};
    std::adjacent_difference(v.begin(), v.end(), v.begin());
 
    for(auto n: v) {
        std::cout << n << ' ';
    }
    std::cout << '\n';
 
    v = {1, 1, 1, 1, 1, 1, 1, 1, 1, 1};
    std::adjacent_difference(v.begin(), v.end()-1, v.begin()+1, std::plus<int>()
 
    for(auto n: v) {
        std::cout << n << ' ';
    }
    std::cout << '\n';
}​

Output:

2 2 2 2 2 2 2 2 2 2
1 1 2 3 5 8 13 21 34 55

See also

partial_sum	computes the partial sum of a range of elements (function template)
accumulate	sums up a range of elements (function template)