map

问题 See below a main() and two very simple classes. Then per Boost serialization (and what is shown) my questions are: 1) Does class B need the normal overloaded stream insertion operators '<<' and '>>' to be defined? Currently in my real code it doesn't have these. 2) Does class A in the store() and load() methods need to iterate through the map and multimap containers explicitely, storing/loading their key:value pairs explicitely? e.g. something like: void A::store(const char* filename){ std:

问题 How to use function as map's key? for example: type Action func(int) func test(a int) { } func test2(a int) { } func main() { x := map[Action]bool{} x[test] = true x[test2] = false } those code would show an error: invalid map key type Action 回答1: You can use reflect . import ( "reflect" "math" ) func foo () { table := make(map[uintptr] string) table[reflect.ValueOf(math.Sin)] = "Sin" table[reflect.ValueOf(math.Cos)] = "Cos" println(table[reflect.ValueOf(math.Cos)]) } 回答2: You cannot use a

问题 I am running a function for several sets of iterables, returning a list of all results as soon as all processes are finished. def fct(variable1, variable2): # do an operation that does not necessarily take the same amount of # time for different input variables and yields result1 and result2 return result1, result2 variables1 = [1,2,3,4] variables2 = [7,8,9,0] with ThreadPoolExecutor(max_workers = 8) as executor: future = executor.map(fct,variables1,variables2) print '[%s]' % ', '.join(map

问题 I am running a function for several sets of iterables, returning a list of all results as soon as all processes are finished. def fct(variable1, variable2): # do an operation that does not necessarily take the same amount of # time for different input variables and yields result1 and result2 return result1, result2 variables1 = [1,2,3,4] variables2 = [7,8,9,0] with ThreadPoolExecutor(max_workers = 8) as executor: future = executor.map(fct,variables1,variables2) print '[%s]' % ', '.join(map

问题 I'm trying to find a efficient way to map a range of values to another value.For example 1-9 -> 49 10-24 ->54 25-49 -> 59 50-74 -> 50 75-99 -> 49 100-150 -> 40 Here the values don't follow any regular patters.One solution is to use conditional statements ( if -else ) but as the set of values increase the number of statements increase and it will be hard to maintain.So is there any other elegant and efficient way to achieve this ? 回答1: Since the ranges are consecutive, you can try to map them

问题 I need a kind of map which is accessible in two directions, so with a key-key structure instead of key-value. Does this exist in Java? If not, what is the best way to create it? So example: mySpecialHashMap.put("key1", "key2"); mySpecialMap.getL2R("key1") returns "key2"; mySpecialMap.getR2L("key2") returns "key1"; 回答1: So you want a bidirectional map. You can use Apache Commons Collections BidiMap or Google Collections BiMap for this. 回答2: You might want to look at BiMap from the Guava

问题 I have a std::map, and I would like to add a valid key to iterate over it later, but without giving any value (it will be given later on in the course of the iterations). This is how I do it for now : std::vector<std::string> valid_keys; //Fill... Then : std::map<std::string, float> map; for(size_t i = 0 ; i < valid_keys.size() ; ++i) { /*I don't want to do that because in fact I don't use a float type*/ map[valid_keys[i]] = 0.f; //<- } //Using : for(std::map<std::string, float>::iterator it

问题 Under the hood, an STL map is a red-black tree, and it uses the < operator of its keys or a user-provided comparison to figure out the location for element insertion. map::find() returns the element that matches the supplied key (if any matches are present) How can it do this without using an equality operator? Let's say my map has the keys 1, 2, 3, and 4 in it. Using only <, I could see that the key 2 should go after 1, after 2, and before 3. But I can't tell whether or not 2 is the same as

问题 I'm creating an iPhone travel app that uses online as well as offline maps. For the offline maps I want to allow users to download an mbtiles file of the area they are interested in (e.g. London). The map should have information such as roads etc.. that are already found in OpenStreetmap. I'm aware of web sites such as http://metro.teczno.com/ for downloading Openstreetmap extracts. What is the easiest way to create mbtiles files of Openstreetmap extracts? Note: no map customization is needed

问题 I'm trying to plot a map of the Pacific using World2Hires in R's mapproj library but there's an odd glitch when I try to fill the countries. How do I fix this? library(maps) library(mapproj) library(mapdata) map("world2Hires", xlim=c(120, 260), ylim=c(-60, 40), boundary=TRUE, interior=TRUE, fill=TRUE, col="gray30", ) map.axes() Here's the output: 回答1: The issue seems to be with a small subset of areas which cause wrapping. From some trial and error saving the original map call like mapnames <