multimap

问题 why does Guava doesn't have the following factory call to create a MultiMap from a normal Map? public static <K,V> MultiMap<K,V> invertMap(Map<V,K> map); I have program-names mapped to an integer of how often they were called. I'd like to invert this, so that i can ultimately construct a TreeMap, sorted by call-count, which then are the keys leading to one or multiple program-names. 回答1: How about: public static <K,V> Multimap<K,V> invertMap(Map<V,K> map) { return Multimaps.invertFrom

问题 I need to implement the overloaded the assignment operator in a class so the vector.erase function will work properly as proposed in the answers to "vector::erase with pointer member". I have implemented also a copy constructor for the same purpose. By the following implementation of the operator I get the warning : 'Player::operator=' : recursive on all control paths, function will cause runtime stack overflow. Apparently the implementation of Player::operator= is incorrect. What is the

问题 I want a custom comparator for the following code. However, I am not allowed to overload operator() , std::less , std::greater . I tried to achieve this using lambda but gcc won't allow me to use auto as a non-static member. Any other way to make this work? #include <iostream> #include <map> #include <set> class Test { public: // bool operator () (const int lhs, const int rhs) { // not allowed // return lhs > rhs; // }; using list = std::multiset<int /*, Test*/>; std::map<const char*, list>

问题 If I have the following piece of code std::unordered_multimap<std::string, std::vector<double>> myMap; std::vector<double> v1, v2, v3; // init v1, v2, v3.... myMap.insert(std::make_pair<std::string, std::vector<double>("vec", v1)); myMap.insert(std::make_pair<std::string, std::vector<double>("vec", v2)); myMap.insert(std::make_pair<std::string, std::vector<double>("vec", v3)); If I access the values with an iterator they will always be in this order: v1, v2, v3 So basically if I insert

问题 I create a MultiMap val ms = new collection.mutable.HashMap[String, collection.mutable.Set[String]]() with collection.mutable.MultiMap[String, String] which, after it has been populated with entries, must be passed to a function that expects a Map[String, Set[String]] . Passing ms directly doesn't work, and trying to convert it into a immutable map via toMap ms.toMap[String, Set[String]] yields Cannot prove that (String, scala.collection.mutable.Set[String]) <:< (String, Set[String]). Can

问题 I need a collection that stores entries as key-value pairs (so I can look up values by a key), but I need one that allows multiple values to share the same key using hibernate 回答1: A map with multiple values for one key is known as a multimap - there's an implementation in the Apache commons library. Hibernate does not support this kind of collection directly, but it can be extended to do so relatively easily by implementing the UserCollectionType interface. This blog article describes how to

问题 Is there an equivalent to the nice MapMaker for MultiMaps? currently i create the cache like this: public static Map<Session,List<Person>> personCache = new MapMaker().weakKeys().makeMap(); the whole point of MultiMap is to avoid the nested List Values. is there any way to construct the multimap with weak keys? 回答1: Unfortunately not. Yet. Could you file a MultimapMaker feature request in our issues db? http://google-collections.googlecode.com 来源： https://stackoverflow.com/questions/737060

问题 Is there any way to elegantly initialize and populate a multi-value Map<K,Collection<V>> using Java 8's stream API? I know it's possible to create a single-value Map<K, V> using the Collectors.toMap(..) functionalities: Stream<Person> persons = fetchPersons(); Map<String, Person> personsByName = persons.collect(Collectors.toMap(Person::getName, Function.identity())); Unfortunately, that method won't work well for possibly non-unique keys such as a person's name. On the other hand, it's

问题 Is there any way to elegantly initialize and populate a multi-value Map<K,Collection<V>> using Java 8's stream API? I know it's possible to create a single-value Map<K, V> using the Collectors.toMap(..) functionalities: Stream<Person> persons = fetchPersons(); Map<String, Person> personsByName = persons.collect(Collectors.toMap(Person::getName, Function.identity())); Unfortunately, that method won't work well for possibly non-unique keys such as a person's name. On the other hand, it's

问题 I try to replace std::multiset with std::priority_queue. But I was dissapointed with the speed results. Running time of the algorithm increase by 50%... Here are the corresponding commands: top() = begin(); pop() = erase(knn.begin()); push() = insert(); I am surprised with the speed of priority_queue implementation, I expected different results (better for PQ)... Conceptually, the multiset is being used as a priority queue. Why are the priority queue and the multiset have such different