std::ranges::set_difference() algorithm
- od C++20
- Simplified
- Detailed
// (1)
constexpr set_difference_result<I1, O>
set_difference( I1 first1, S1 last1, I2 first2, S2 last2, O result,
Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {} );
// (2)
constexpr set_difference_result<ranges::borrowed_iterator_t<R1>, O>
set_difference( R1&& r1, R2&& r2, O result, Comp comp = {},
Proj1 proj1 = {}, Proj2 proj2 = {} );
The type of arguments are generic and have the following constraints:
I1
,I2
-std::input_iterator
S1
,S2
-std::sentinel_for<I1>
,std::sentinel_for<I2>
R1
,R2
-std::ranges::input_range
O
-std::weakly_incrementable
Comp
- (none)Proj1
,Proj2
- (none)
The Proj
and Comp
template arguments have the following default types: std::identity
, ranges::less
for all overloads.
Additionaly, each overload has the following constraints:
- (1) -
mergeable<I1, I2, O, Comp, Proj1, Proj2>
- (2) -
mergeable<ranges::iterator_t<R1>, ranges::iterator_t<R2>, O, Comp, Proj1, Proj2>
(The std::
namespace was ommited here for readability)
// (1)
template<
std::input_iterator I1,
std::sentinel_for<I1> S1,
std::input_iterator I2,
std::sentinel_for<I2> S2,
std::weakly_incrementable O,
class Comp = ranges::less,
class Proj1 = std::identity,
class Proj2 = std::identity
>
requires std::mergeable<I1, I2, O, Comp, Proj1, Proj2>
constexpr set_difference_result<I1, O>
set_difference( I1 first1, S1 last1, I2 first2, S2 last2, O result,
Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {} );
// (2)
template<
ranges::input_range R1,
ranges::input_range R2,
std::weakly_incrementable O,
class Comp = ranges::less,
class Proj1 = std::identity,
class Proj2 = std::identity
>
requires std::mergeable<ranges::iterator_t<R1>, ranges::iterator_t<R2>,
O, Comp, Proj1, Proj2>
constexpr set_difference_result<ranges::borrowed_iterator_t<R1>, O>
set_difference( R1&& r1, R2&& r2, O result, Comp comp = {},
Proj1 proj1 = {}, Proj2 proj2 = {} );
With the helper types defined as follows:
template< class I, class O >
using set_difference_result = ranges::in_out_result<I, O>;
Copies the elements from the sorted input range [first1
; last1
)
which are not found in the sorted input range [first2
; last2
) to the output range beginning at result
.
- (1) Elements are compared using the given binary comparison function
comp
. - (2) Same as (1), but uses
r1
as the first range andr2
as the second range, as if usingranges::begin(r1)
asfirst1
,ranges::end(r1)
aslast1
,ranges::begin(r2)
asfirst2
, andranges::end(r2)
aslast2
.
The behavior is undefined
if:- The input ranges are not sorted with respect to
comp
andproj1
orproj2
, respectively - Or the resulting range overlaps with either of the input ranges.
The function-like entities described on this page are niebloids.
Parameters
first1 last1 | The first sorted input range. |
r r1 | The first sorted input range. |
first2 last2 | The second sorted input range. |
r2 | The second sorted input range. |
result | The beginning of the destination range. |
comp | Comparator to apply to the projected elements. |
proj1 | Projection to apply to the elements in the first range. |
proj2 | Projection to apply to the elements in the second range. |
Return value
A value of type ranges::set_difference_result
initialized as follows:
{
last1,
result_last
}
Where result_last
is the end of the constructed range.
Complexity
Given N1
as ranges::distance(first1, last1)
and N2
as ranges::distance(first2, last12)
:
2 * (N1 + N2) − 1 comparisons and applications of each projection.
Exceptions
(none)
Possible implementation
set_difference(1) and set_difference(2)
struct set_difference_fn
{
template<std::input_iterator I1, std::sentinel_for<I1> S1,
std::input_iterator I2, std::sentinel_for<I2> S2,
std::weakly_incrementable O, class Comp = ranges::less,
class Proj1 = std::identity, class Proj2 = std::identity >
requires std::mergeable<I1, I2, O, Comp, Proj1, Proj2>
constexpr ranges::set_difference_result<I1, O>
operator()(I1 first1, S1 last1, I2 first2, S2 last2,
O result, Comp comp = {},
Proj1 proj1 = {}, Proj2 proj2 = {}) const
{
while (!(first1 == last1 or first2 == last2))
{
if (std::invoke(comp, std::invoke(proj1, *first1), std::invoke(proj2, *first2)))
{
*result = *first1;
++first1;
++result;
}
else if (std::invoke(comp, std::invoke(proj2, *first2),
std::invoke(proj1, *first1)))
{
++first2;
}
else
{
++first1;
++first2;
}
}
return ranges::copy(std::move(first1), std::move(last1), std::move(result));
}
template<ranges::input_range R1, ranges::input_range R2,
std::weakly_incrementable O, class Comp = ranges::less,
class Proj1 = std::identity, class Proj2 = std::identity>
requires std::mergeable<ranges::iterator_t<R1>, ranges::iterator_t<R2>,
O, Comp, Proj1, Proj2>
constexpr ranges::set_difference_result<ranges::borrowed_iterator_t<R1>, O>
operator()(R1&& r1, R2&& r2, O result, Comp comp = {},
Proj1 proj1 = {}, Proj2 proj2 = {}) const
{
return (*this)(ranges::begin(r1), ranges::end(r1),
ranges::begin(r2), ranges::end(r2),
std::move(result), std::move(comp),
std::move(proj1), std::move(proj2));
}
};
inline constexpr set_difference_fn set_difference {};
Examples
#include <algorithm>
#include <cassert>
#include <iostream>
#include <iterator>
#include <string_view>
#include <vector>
auto print = [](const auto& v, std::string_view end = "")
{
for (std::cout << "{ "; auto i : v)
std::cout << i << ' ';
std::cout << "} " << end;
};
struct Order // a struct with some very interesting data
{
int order_id {};
friend std::ostream& operator<<(std::ostream& os, const Order& ord)
{
return os << "{" << ord.order_id << "},";
}
};
int main()
{
const auto v1 = {1, 2, 5, 5, 5, 9};
const auto v2 = {2, 5, 7};
std::vector<int> diff {};
std::ranges::set_difference(v1, v2, std::back_inserter(diff));
print(v1, "∖ ");
print(v2, "= ");
print(diff, "\n");
// we want to know which orders "cut" between old and new states:
const std::vector<Order> old_orders { {1}, {2}, {5}, {9}, };
const std::vector<Order> new_orders { {2}, {5}, {7}, };
std::vector<Order> cut_orders(old_orders.size() + new_orders.size());
auto [old_orders_end, cut_orders_last] =
std::ranges::set_difference(old_orders, new_orders,
cut_orders.begin(), {},
&Order::order_id, &Order::order_id);
assert(old_orders_end == old_orders.end());
std::cout << "old orders = "; print(old_orders, "\n");
std::cout << "new orders = "; print(new_orders, "\n");
std::cout << "cut orders = "; print(cut_orders, "\n");
cut_orders.erase(cut_orders_last, end(cut_orders));
std::cout << "cut orders = "; print(cut_orders, "\n");
}
{ 1 2 5 5 5 9 } ∖ { 2 5 7 } = { 1 5 5 9 }
old orders = { {1}, {2}, {5}, {9}, }
new orders = { {2}, {5}, {7}, }
cut orders = { {1}, {9}, {0}, {0}, {0}, {0}, {0}, }
cut orders = { {1}, {9}, }
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