使用 Boost Multi-Index 搜索多个索引
如何根据先前搜索的结果限制 boost::multi_index 中的搜索？ 举个例子：假设我有一个具有如下内部值的矩形类：
class MyRect
{
public:
int width;
int height;
double value;
}
并且我需要此类对象的数据结构来回答诸如“给定一个 input_rectangle - 哪个对象 MyRect 包含在该矩形中并且具有最高值？”
我可以使用这样的“multi_index”：
struct given_value{};
struct given_width{};
struct given_height{};
typedef multi_index_container<MyRect,
indexed_by<
ordered_non_unique< tag<given_value>,
member<MyRect, double, &MyRect::value>,
ordered_non_unique< tag<given_width>,
member<MyRect, int, &MyRect::width>,
ordered_non_unique< tag<given_height>,
member<MyRect, int, &MyRect::height>, >
>
> MyDataStructure;
typedef MyDataStructure::index<given_width>::type MyDataStructureGivenWidth;
typedef MyDataStructureGivenWidth::iterator WidthIterator;
如果我的 input_rectangle 有宽度 input_width 我可以使用这样的东西：
WidthIterator start_iter = data_object.get<given_width>().begin();
WidthIterator end_iter = data_object.get<given_width>().upper_bound(input_width);
但是我如何限制对 coresp 高度的搜索两个给定的迭代器？ （然后找到该结果中具有最高值的对象？）
how do I limit the search in a boost::multi_index by the result of a previous search?
As an example: suppose I have a rectangle class with an internal value like this:
class MyRect
{
public:
int width;
int height;
double value;
}
and I need a data structure of such object to answer queries like "given an input_rectangle - which object MyRect is contained in that rectangle and has the highest value?"
I could use a 'multi_index' like this:
struct given_value{};
struct given_width{};
struct given_height{};
typedef multi_index_container<MyRect,
indexed_by<
ordered_non_unique< tag<given_value>,
member<MyRect, double, &MyRect::value>,
ordered_non_unique< tag<given_width>,
member<MyRect, int, &MyRect::width>,
ordered_non_unique< tag<given_height>,
member<MyRect, int, &MyRect::height>, >
>
> MyDataStructure;
typedef MyDataStructure::index<given_width>::type MyDataStructureGivenWidth;
typedef MyDataStructureGivenWidth::iterator WidthIterator;
If my input_rectangle has width input_width I could use something like this:
WidthIterator start_iter = data_object.get<given_width>().begin();
WidthIterator end_iter = data_object.get<given_width>().upper_bound(input_width);
But how do I limit the search for the coresp height by the two given iterators?
(And after that find the object with the highest value in that result?)
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我认为您无法进行就地限制。
将匹配宽度查询的结果迭代器存储在另一个容器中，并使用该容器通过remove_if 查找匹配高度。然后使用 max_element 找到最大的。
如果将元素存储为指针，则可以使用相同的 MIC 来存储结果。
I don't think you can do an inplace limitation.
Store the resulting iterators of the matching widths query in another container and use that container to find the matching heights with remove_if. Then use max_element to find the largest.
If you store the elements as pointers, you could use the same MIC to store the results.
如果我正确理解你的问题，可能会有一个更简单的解决方案。只需将您的 MyRect 放入按值排序的 STL-Set 中（需要定义比较运算符或自定义比较函数）。您可以创建一个自定义谓词并使用它来检查给定的 MyRect 是否在特定范围内。然后使用 STL 算法
find_if，并将自定义谓词交给它。如果您确保它以降序遍历序列（例如通过使用reverse_iterator），它应该返回您正在寻找的MyRect。希望这是可以理解的并且适用于您的问题。
If I understand your problem correctly, there may be a simpler solution. Just put your MyRects into an STL-Set ordered by value (need to define comparison operator or custom comparison function). The you can create a custom predicate that and use that checks if a given MyRect is within a certain range. Then you use the STL-Algorithm
find_if, and hand it the custom predicate. If you make sure that it traverses the sequence in decreasing order (e.g. by using reverse_iterator), it should return the MyRect you are looking for.Hope that is understandable and applies to your problem.