multimap

Is it possible to have multiple values for the same key in a hash table? If not, can you suggest any such class or interface which could be used? No. That's kind of the idea of hash tables. However, you could either roll your own with a Map<YourKeyObject, List<YourValueObject>> and some utility methods for creating the list if it's not present, or use something like the Multimap from Google Collections . Example: String key = "hello"; Multimap<String, Integer> myMap = HashMultimap.create(); myMap.put(key, 1); myMap.put(key, 5000); System.out.println(myMap.get(key)); // prints either "[1, 5000]

For example a C++ vector is implemented using a dynamic array where each element uses consecutive memory spaces. I know that a C++ multimap is a one to many relationship but what is the internal structure? The C++ standard does not define how the standard containers should be implemented, it only gives certain constraints like the one you say for vectors. multimaps have certain runtime complexity (O(lg n) for the interesting operations) and other guarantees, and can be implemented as red-black trees . This is how they are implemented in the GNU standard C++ library. Oliver Charlesworth Very

I have a rather large amount of data to analyse - each file is about 5gigs. Each file is of the following format: xxxxx yyyyy Both key and value can repeat, but the keys are sorted in increasing order. I'm trying to use a memory mapped file for this purpose and then find the required keys and work with them. This is what I've written: if (data_file != "") { clock_start = clock(); data_file_mapped.open(data_file); data_multimap = (std::multimap<double, unsigned int> *)data_file_mapped.data(); if (data_multimap != NULL) { std::multimap<double, unsigned int>::iterator it = data_multimap->find

I have some data which come with a integer index. I am continuous generating new data which needs to added to the collection of data I have, sorted by that index, at the same time I want to easily be able to go the start of the data and iterate through it. This sounds like std::multimap is just what I need. However, I also need data with the same index to be kept in the order in which it was inserted, in this case meaning that when I iterate through the data I get to the earlier data before the later data. Does multimap do this? I haven't found any guarantees that this is the case. In the sgi

I didn't find such a multimap construction... When I want to do this, I iterate over the map, and populate the multimap. Is there an other way? final Map<String, Collection<String>> map = ImmutableMap.<String, Collection<String>>of( "1", Arrays.asList("a", "b", "c", "c")); System.out.println(Multimaps.forMap(map)); final Multimap<String, String> expected = ArrayListMultimap.create(); for (Map.Entry<String, Collection<String>> entry : map.entrySet()) { expected.putAll(entry.getKey(), entry.getValue()); } System.out.println(expected); The first result is {1=[[a, b, c, c]]} but I expect {1=[a, b,

Is there a simple or standard way to have a multimap iterator which iterate across unique keys in a multimap? i.e. for a set that looks like: {1, "a"}, {1, "lemon"}, {2, "peacock"}, {3, "angel"} an iterator which would start at {1, "a"} then incrementing would point to {2, "peacock"} and then incrementing again would point to {3, "angel"} ? Pablo You can use upper_bound to increment the iterator position instead of ++ : #include <map> #include <string> #include <iostream> using namespace std; int main() { multimap<int,string> mm; mm.insert(make_pair(1, "a")); mm.insert(make_pair(1, "lemon"));