multimap

问题 C++ standard for "26.4.5.1 Class template multimap overview" p1 says: A multimap is an associative container that supports equivalent keys (possibly containing multiple copies of the same key value ) and provides for fast retrieval of values of another type T based on the keys. emphasis is mine. So does it mean that std::multimap may not keep a copy of original key object when inserted into equal range and replace it with equal one? PS To make clear this question is inspired by this Does Each

问题 Instead of implementing my own I was wondering if anyone knows of a histogram or bag datastructure implementation in Objective-C that I can use. Essentially a histogram is a hashmap of lists where the lists contain values that relate to their hash entry. A good example is a histogram of supermarket items where you place each group of items dairy, meat, canned goods in their own bag. You can then very easily access each group of items according to their type. 回答1: NSCountedSet is a multiset

问题 I would like to count the number of entries between two iterators of an std::multimap in less than O(N) time. Are there any tricks or clever ways to do this? Since std::multimap has bidirectional iterators, my understanding is that something like std::distance could do this in O(N) time. Additional details: The multimap 's key is an N-tuple. I'm trying to find the number of entries in the multimap whose key's first element is 0. The options for the first element of they key are 0 and 1, and

问题 I can't imagine this hasn't been asked, but I'm not having any luck finding it. Does each element of a multimap contain its value and its key? That is does the internal structure of a multimap look like more like this: map<key, vector<value>> Or more like this: vector<pair<key, value>> 回答1: Each element contains both its key and value. You can tell because iteration returns a stable non-allocating reference to std::pair<Key const, Value> . What more, Keys can compare equal but be different. A

问题 I need a collection that behaves something like C++ multimap, but I also need to be able to get elements by a range of keys. 回答1: There is no built-in multimap collection in Java. To solve this you can map to every key a list of values: Map<String, List<String>> , for example. Otherwise there are third-party libraries with implemented multimaps - here is one of them. 回答2: You can look into Google Collections. It has multiple implementations for MultiMap . 回答3: There is a simple hack around

问题 Say I have a guava Multimap. I have a value, "Foo", that may belong to one or more keys. Is there any way I can figure out which keys contain an entry "Foo"? 回答1: You can invert the Multimap. For this you can use the method Multimaps.invertFrom. For example, if your Multimap is a Multimap<String, String> Multimap<String, String> invertedMultimap = Multimaps.invertFrom(myMultimap, ArrayListMultimap.<String, String>create()); 回答2: If you have an ImmutableMultimap , which is a good idea whenever

问题 I'm trying to convert a MultiMap of billions of data values to a Spark DataFrame to run calculations on then write the results to a cassandra table. I generate the multimap from the following cassandra query and loop. I'd be happy to take suggestions if there would be a better way to get and manipulate this data into a DataFrame like I am with the loop. Code Updated With Answer: //Build ResultSet from cassandra query for data manipulation. Statement stmt = new SimpleStatement("SELECT \"Power\

问题 I am looking for the perfect data structure for the following scenario: I have an index i , and for each one I need to support the following operation 1 : Quickly look up its Foo objects (see below), each of which is associated with a double value. So I did this: struct Foo { int a, b, c; }; typedef std::map<Foo, double> VecElem; std::vector<VecElem> vec; But it turns out to be inefficient because I also have to provide very fast support for the following operation 2 : Remove all Foo s that

问题 Is it possible to have multiple values, for a single key, in the Java dictionary class? 回答1: First, regarding the dictionary class: That class is considered obselete, the documentation recommends using Map instead. This kind of collection you are seeking is called a multimap. You could implement one yourself with a list, but that is tedious. You may want to use a MultiMap from either Apache Collections or from the Google Collections. While I am personally a fan of the apache collections, they

问题 I created a Multimap Multimap<Integer, String> mhm= ArrayListMultimap.create(); my numbers range from 0 to 2400. I have inserted data like mhm.put(800 ,"A") mhm.put(1200 ,"B") mhm.put(1200 ,"A") mhm.put(1500 ,"B") mhm.put(600 ,"A") mhm.put(700 ,"B") mhm.put(1200 ,"A") mhm.put(1201 ,"B") I want to sort the Multimap on key field that is Integer? There are not much posts on satckoverflow which tells how to do this. expected output: mhm.put(600 ,"A") mhm.put(700 ,"B") mhm.put(800 ,"A") mhm.put