[英]How can I Iterate over Vertices & Edges in an Order Provided by a (Bundled) Property, in the BGL?
說我有一些提升圖
#include <boost/graph/adjacency_list.hpp>
struct Vertex {
double property_1;
int property_2;
};
using Graph_t = boost::adjacency_list<boost::listS,
boost::listS,
boost::undirectedS,
Vertex,
boost::no_property>;
Graph_t g(5);
現在想以不同的順序迭代頂點,比如:
property_2
降序property_1
升序我如何以最有效的方式做到這一點?
到目前為止,我創建了帶有屬性的std::vector
和包含索引的向量,並按屬性對它們進行了排序。 但是,如果您有許多屬性可以創建大量可以避免的結構。
我還查看了boost::multi_index
映射,就像在這個 cplusplus.com 問題中一樣,但這對我來說似乎也不苗條。
我怎樣才能做到這一點? 對任何提示感到高興!
Boost.MultiIndex 可以以一種相當復雜的、未記錄的方式插入:
#include <boost/graph/adjacency_list.hpp>
#include <boost/multi_index_container.hpp>
#include <boost/multi_index/random_access_index.hpp>
#include <boost/multi_index/ordered_index.hpp>
struct mic_tag:
/* it is assumed first index is random-access */
virtual public boost::graph_detail::random_access_container_tag,
virtual public boost::graph_detail::back_insertion_sequence_tag{};
namespace boost{
template<typename... Args>
mic_tag container_category(boost::multi_index_container<Args...>&){return {};}
}
template<typename GraphType,typename KeyExtractor>
struct vertex_adapted
{
using result_type=typename KeyExtractor::result_type;
decltype(auto) operator()(void* p)const
{
return key(
static_cast<typename GraphType::stored_vertex*>(p)->m_property);
}
KeyExtractor key;
};
struct vertex_t
{
double property_1;
int property_2;
};
struct graph_t;
struct graph_t_vertex_list;
namespace boost{
template<typename Value>
struct container_gen<graph_t_vertex_list,Value>
{
using type=boost::multi_index_container<
Value,
boost::multi_index::indexed_by<
boost::multi_index::random_access<>,
boost::multi_index::ordered_non_unique<
vertex_adapted<
graph_t,
boost::multi_index::member<vertex_t,double,&vertex_t::property_1>
>
>,
boost::multi_index::ordered_non_unique<
vertex_adapted<
graph_t,
boost::multi_index::member<vertex_t,int,&vertex_t::property_2>
>,
std::greater<int>
>
>
>;
};
}
struct graph_t:
boost::adjacency_list<
boost::listS,
graph_t_vertex_list,
boost::undirectedS,
vertex_t
>{};
/* testing */
#include <iostream>
std::ostream& operator<<(std::ostream& os,const vertex_t& v)
{
os<<"{"<<v.property_1<<","<<v.property_2<<"}";
return os;
}
int main()
{
graph_t g;
add_vertex(vertex_t{0.0,0},g);
add_vertex(vertex_t{0.1,1},g);
add_vertex(vertex_t{0.2,2},g);
for(void* p:g.m_vertices.get<1>()){
std::cout<<static_cast<graph_t::stored_vertex*>(p)->m_property;
}
std::cout<<"\n";
for(void* p:g.m_vertices.get<2>()){
std::cout<<static_cast<graph_t::stored_vertex*>(p)->m_property;
}
std::cout<<"\n";
}
Output
{0,0}{0.1,1}{0.2,2}
{0.2,2}{0.1,1}{0,0}
4 月 14 日更新:我對事情進行了一些重構,以便生成的用戶代碼更加直接:
struct vertex_t
{
double property_1;
int property_2;
};
using graph_t= boost::adjacency_list<
boost::listS,
mic_listS<
boost::multi_index::ordered_non_unique<
boost::multi_index::member<vertex_t,double,&vertex_t::property_1>
>,
boost::multi_index::ordered_non_unique<
boost::multi_index::member<vertex_t,int,&vertex_t::property_2>,
std::greater<int>
>
>,
boost::undirectedS,
vertex_t
>;
完整代碼如下:
#include <boost/graph/adjacency_list.hpp>
#include <boost/multi_index_container.hpp>
#include <boost/multi_index/random_access_index.hpp>
template<typename KeyExtractor>
struct mic_list_key_extractor
{
using result_type=typename KeyExtractor::result_type;
template<typename StoredVertex>
decltype(auto) operator()(StoredVertex& v)const{return key(v.m_property);}
KeyExtractor key;
};
template<typename IndexSpecifier,typename=void>
struct mic_list_index_specifier{using type=IndexSpecifier;};
template<
template<typename...> class IndexSpecifier,
typename Arg1,typename Arg2,typename... Args
>
struct mic_list_index_specifier<
IndexSpecifier<Arg1,Arg2,Args...>,
std::void_t<typename IndexSpecifier<Arg1,Arg2,Args...>::key_from_value_type>>
{
static constexpr bool has_tag=boost::multi_index::detail::is_tag<Arg1>::value;
using arg1=std::conditional_t<has_tag,Arg1,mic_list_key_extractor<Arg1>>;
using arg2=std::conditional_t<has_tag,mic_list_key_extractor<Arg2>,Arg2>;
using type=IndexSpecifier<arg1,arg2,Args...>;
};
template<typename IndexSpecifier>
using mic_list_index_specifier_t=
typename mic_list_index_specifier<IndexSpecifier>::type;
template<typename Value,typename... IndexSpecifiers>
struct mic_list:boost::multi_index_container<
Value,
boost::multi_index::indexed_by<
boost::multi_index::random_access<>,
mic_list_index_specifier_t<IndexSpecifiers>...
>
>
{};
template<typename... IndexSpecifiers>
struct mic_listS;
struct mic_list_tag:
virtual public boost::graph_detail::random_access_container_tag,
virtual public boost::graph_detail::back_insertion_sequence_tag{};
namespace boost{
template<typename... Args>
mic_list_tag container_category(const mic_list<Args...>&){return {};}
template<typename Value,typename... IndexSpecifiers>
struct container_gen<mic_listS<IndexSpecifiers...>,Value>
{
using type=mic_list<Value,IndexSpecifiers...>;
};
namespace detail
{
template<typename... IndexSpecifiers>
struct is_random_access<mic_listS<IndexSpecifiers...>>
{
static constexpr bool value=true;
using type=boost::mpl::true_;
};
}
}
/* testing */
#include <boost/multi_index/ordered_index.hpp>
#include <iostream>
struct vertex_t
{
double property_1;
int property_2;
};
using graph_t= boost::adjacency_list<
boost::listS,
mic_listS<
boost::multi_index::ordered_non_unique<
boost::multi_index::member<vertex_t,double,&vertex_t::property_1>
>,
boost::multi_index::ordered_non_unique<
boost::multi_index::member<vertex_t,int,&vertex_t::property_2>,
std::greater<int>
>
>,
boost::undirectedS,
vertex_t
>;
std::ostream& operator<<(std::ostream& os,const vertex_t& v)
{
os<<"{"<<v.property_1<<","<<v.property_2<<"}";
return os;
}
int main()
{
graph_t g;
add_vertex(vertex_t{0.0,0},g);
add_vertex(vertex_t{0.1,1},g);
add_vertex(vertex_t{0.2,2},g);
for(const auto& v:g.m_vertices.get<1>()){
std::cout<<v.m_property;
}
std::cout<<"\n";
for(const auto& v:g.m_vertices.get<2>()){
std::cout<<v.m_property;
}
std::cout<<"\n";
}
Output
{0,0}{0.1,1}{0.2,2}
{0.2,2}{0.1,1}{0,0}
這(顯然)不是圖書館的特色。
但是,您可以使用范圍或范圍適配器,就像在任何其他情況下一樣:
#include <boost/graph/adjacency_list.hpp>
#include <boost/range/adaptors.hpp>
#include <boost/range/algorithm.hpp>
#include <boost/range/algorithm_ext.hpp>
#include <fmt/ranges.h>
#include <fmt/ostream.h>
#include <random>
struct Vertex {
double property_1;
int property_2;
};
static inline std::ostream& operator<<(std::ostream& os, Vertex const& v) {
return os << "V(" << v.property_1 << ", " << v.property_2 << ")";
}
using Graph_t =
boost::adjacency_list<boost::listS, boost::listS, boost::undirectedS,
Vertex, boost::no_property>;
int main() {
using boost::make_iterator_range;
using namespace boost::adaptors;
Graph_t g(5);
int i = 0;
for (auto& v : make_iterator_range(vertices(g))) {
++i;
g[v] = {i / -.3, i * 11};
}
auto get_bundle = [&g](auto v) -> auto& { return g[v]; };
fmt::print("Natural order: {}\n",
make_iterator_range(vertices(g)));
fmt::print("Natural order: {}\n",
make_iterator_range(vertices(g) | transformed(get_bundle)));
fmt::print(
"Reverse natural order: {}\n",
make_iterator_range(vertices(g) | transformed(get_bundle) | reversed));
auto make_view = [=](auto range) {
return std::vector<std::reference_wrapper<Vertex>>(
begin(range), end(range));
};
auto view =
make_view(make_iterator_range(vertices(g) | transformed(get_bundle)));
boost::reverse(view);
fmt::print("view: {}\n", view);
boost::reverse(view);
fmt::print("reversed: {}\n", view);
auto less_by = [](auto member) {
return [=, prj = std::mem_fn(member)](auto const& a, auto const& b) {
return prj(a) < prj(b);
};
};
boost::sort(view, less_by(&Vertex::property_1));
fmt::print("less_by property_1: {}\n", view);
boost::sort(view, less_by(&Vertex::property_2));
fmt::print("less_by property_2: {}\n", view);
{
static std::random_device rd;
static std::mt19937 randgen{rd()};
std::shuffle(view.begin(), view.end(), randgen);
fmt::print("random order: {}\n", view);
}
// just a loop is also fine, of course
i = 0;
for (Vertex& bundle : view) {
bundle.property_2 = i++;
}
fmt::print("modified: {}\n", view);
}
印刷
Natural order: {0x1467eb0, 0x1467f10, 0x1467f70, 0x1467fd0, 0x1468030}
Natural order: {V(-3.33333, 11), V(-6.66667, 22), V(-10, 33), V(-13.3333, 44), V(-16.6667, 55)}
Reverse natural order: {V(-16.6667, 55), V(-13.3333, 44), V(-10, 33), V(-6.66667, 22), V(-3.33333, 11)}
view: {V(-16.6667, 55), V(-13.3333, 44), V(-10, 33), V(-6.66667, 22), V(-3.33333, 11)}
reversed: {V(-3.33333, 11), V(-6.66667, 22), V(-10, 33), V(-13.3333, 44), V(-16.6667, 55)}
less_by property_1: {V(-16.6667, 55), V(-13.3333, 44), V(-10, 33), V(-6.66667, 22), V(-3.33333, 11)}
less_by property_2: {V(-3.33333, 11), V(-6.66667, 22), V(-10, 33), V(-13.3333, 44), V(-16.6667, 55)}
random order: {V(-13.3333, 44), V(-3.33333, 11), V(-10, 33), V(-6.66667, 22), V(-16.6667, 55)}
modified: {V(-13.3333, 0), V(-3.33333, 1), V(-10, 2), V(-6.66667, 3), V(-16.6667, 4)}
std::ranges 可以為您提供其中的大部分,但根據我的經驗,還有一些限制。 但是,它通常會更安全(因為 Boost Range V2 已經很老了)。
擁有“活動索引”(如數據庫)使您的頂點容器選擇器 select 成為多索引容器。 請參閱此處的建議https://marc.info/?l=boost&m=118835654637830
到 model 您自己的圖形數據結構,請參閱此處獲取靈感
作為對評論的回應,您可以使用 Boost PFR 靜態生成具有比較器簡單類型的數組:
template <typename T, typename Op = std::less<> >
constexpr static inline auto make_field_comparers(Op op = {}) {
namespace pfr = boost::pfr;
auto constexpr N = pfr::tuple_size<T>::value;
using A = std::array<std::function<bool(T const&, T const&)>, N>;
auto lift = [op](auto prj) {
return [=](T const& a, T const& b) { return op(prj(a), prj(b)); };
};
return [lift]<size_t... I>(std::index_sequence<I...>){
return A{lift([](T const& v) { return pfr::get<I>(v); })...};
}
(std::make_index_sequence<N>{});
}
您可以使用Live On Compiler Explorer
std::vector orderings {
std::pair { "asc", make_field_comparers<Vertex>() },
std::pair { "desc", make_field_comparers<Vertex>(std::greater<>{}) },
};
for (auto const& [dir, fields] : orderings) {
for (size_t field = 0; field < fields.size(); ++field) {
boost::sort(view, fields[field]);
fmt::print("by field #{} {}: {}\n", field, dir, view);
}
}
印刷
by field #0 asc: {V(-16.6667, 55), V(-13.3333, 44), V(-10, 33), V(-6.66667, 22), V(-3.33333, 11)}
by field #1 asc: {V(-3.33333, 11), V(-6.66667, 22), V(-10, 33), V(-13.3333, 44), V(-16.6667, 55)}
by field #0 desc: {V(-3.33333, 11), V(-6.66667, 22), V(-10, 33), V(-13.3333, 44), V(-16.6667, 55)}
by field #1 desc: {V(-16.6667, 55), V(-13.3333, 44), V(-10, 33), V(-6.66667, 22), V(-3.33333, 11)}
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.