map

问题 I looking for an on-the-shelf way to convert a List into a Map in Dart. In python for example you can do: l= [ ('a',(1,2)), ('b',(2,3)), ('c',(3,4) ) ] d=dict(l) ==> {'a': (1, 2), 'c': (3, 4), 'b': (2, 3)} The dict function expects a List of couple. For each couple, the first element is used as the key and the second as the data. In Dart I saw the following method for a List : asMap() , but it's not doing what i expect: it use the list index as key. My questions: Do you known anything in Dart

问题 I have data that's in a map, and I want to index into the map by key to get a value. mdi, err := page.Metadata() fmt.Println(mdi["title"]) However I keep getting the error message invalid operation: mdi["title"] (type interface {} does not support indexing) . I am confused, because the data is a map and I should be able to index into it to get the value. In case the type wasn't clear, I also tried to cast the value to a string: title, ok := mdi["title"].(string) checkOk(ok) fmt.Println(title)

问题 I have data that's in a map, and I want to index into the map by key to get a value. mdi, err := page.Metadata() fmt.Println(mdi["title"]) However I keep getting the error message invalid operation: mdi["title"] (type interface {} does not support indexing) . I am confused, because the data is a map and I should be able to index into it to get the value. In case the type wasn't clear, I also tried to cast the value to a string: title, ok := mdi["title"].(string) checkOk(ok) fmt.Println(title)

问题 One can iterate through a SortedMap by using the iterator from myMap.entrySet().iterator() . But does this iterator preserve the ordering of the sorted map object ? The SortedMap interface has no own methods to iterate through the entries. What is the standard way to iterate ordered through the entries ? 回答1: The standard iterator is guaranteed to keep the iteration order exactly the same as the natural order of the keys, for both keys and entries. This is stated in the documentation and can

问题 I am trying to lazy-load data from the server into a Map. For that reason I would like to add functionality to Map, so that when a key doesn't exist, a call is done to get the value . What I tried is this: class LazyMap extends Map { // use .length for now. When this works, go use xhr operator [](key) => LazyMap.putIfAbsent(key, () => key.length); } LazyMap test = new LazyMap(); main() { print(test.containsKey('hallo')); // false // I prefer to use this terse syntax and not have to use

问题 I'm working on a top-down rpg, and want to implement seamless scrolling maps. That is, as the player explores the world, there is no loading screen between maps and no "doors" to the next area. I have two ways to break down the world. At the top level, I have "zones" which is simply a collection of 9 "maps"(These zones are only represented by directories). Within the zone, the 9 maps are organized into a 3x3 grid. I haven't figured out the best way to represent these maps yet, whether it's by

问题 I might be confused between hashmap in Java, and map / dict in Python. I thought that the hash (k/v abstraction) of Java is kind of the same as dict in Python But then what does the map datatype do? Is it the same abstraction as the hashmap abstraction? If so, then how is it different from dictionary? I went through the docs, but it took me to whole together different paradigm: functional programming. 回答1: Map is not a datatype in python. It applies a function to a series of values and

问题 I might be confused between hashmap in Java, and map / dict in Python. I thought that the hash (k/v abstraction) of Java is kind of the same as dict in Python But then what does the map datatype do? Is it the same abstraction as the hashmap abstraction? If so, then how is it different from dictionary? I went through the docs, but it took me to whole together different paradigm: functional programming. 回答1: Map is not a datatype in python. It applies a function to a series of values and

问题 My map is defined as such: map<string, LocationStruct> myLocations; where the key is a time string I am only keeping 40 items in this map, and would like to drop off the last item in the map when i reach 40 items. I know that i can't do myLocations.erase(myLocations.end()) , so how do i go about this? I do intend for the last item in the map to be the oldest, and therefore FIFO. The data will be coming in rather quick (about 20Hz), so i'm hoping that the map can keep up with it. I do need to

问题 val m = scala.collection.mutable.Map[String, Int]() // this doesn't work m += ("foo", 2) // this does work m += (("foo", 2)) // this works too val barpair = ("bar", 3) m += barpair So what's the deal with m += ("foo" , 2) not working? Scala gives the type error: error: type mismatch; found : java.lang.String("foo") required: (String, Int) m += ("foo", 2) ^ Apparently Scala thinks that I am trying to call += with two arguments, instead of one tuple argument. Why? Isn't it unambiguous, since I