set

问题 I have a set of data which in some occasion I need to sort them in one way and some occasion in another way. For example, suppose the data set is a set of strings,{"abc", "dfg",...}. Sometimes I need to sort them in alphabetic order and sometimes by comparing their length. Initially I used std::set as a container of my data and implemented 2 comparators, hoping that I can change the comparator of the set on the fly, cause the data is huge and it's not a good idea to copy it from one set to

问题 Why is set.begin() always returning a const iterator and not a standard one? 35 int test(){ 36 std::set<int> myset; 37 myset.insert(2); 38 myset.insert(3); 39 int &res = *myset.begin(); 40 return res; 41 } test.cpp:39: error: invalid initialization of reference of type ‘int&’ from expression of type ‘const int’ 回答1: It's not returning a const_iterator , rather the key_type of std::set<int> is const int . Remember that keys in a std::set are constant. You can't change a key after it's inserted

问题 This question already has answers here : Closed 9 years ago . Possible Duplicate: Comparing two collections for equality I need to verify if two IEnumerable<T> lists have the same elements, not necessarily in the same order. I'm targetting .NET 3.5. Here are the tests. The question is, how should HasSameElements() be implemented? var l1 = new[]{1,2,3}; var l2 = new[]{3,1,2}; bool rez1 = l1.HasSameElements(l2);//should be true var l3 = new[]{1,2,3,2}; var l4 = new[]{3,1,2,2}; bool rez2 = l3

问题 Edit: explained the problem properly now. I have a hashmap where i want to store sets of words seen together (key) and the lines in which they were seen together(value). This is the structure i came up with: HashMap<HashSet<String>, HashSet<Integer>> hm= ... for inputs: mango, banana, apple apple, banana peach, walrus walrus, peach As I read this, line by line, I make new temporary keys (hashsets not yet inserted into hashmap) from the combination of words in the line. Each temporary key is a

问题 I am working on a Django project and I want to send a signal when something gets added to some model's related set. E.g. we have an owner who has a set of collectables, and each time the method owner.collectable_set.add(something) is getting called, I want a signal like collectable_added or something. Signals are clear to me, but I don't know which manager(?) contains the "add" method that I want to override. Edit for Xavier's request to provide more details: you can easily override a model’s

问题 I have a set that I've added a list to. var a = new Set(); a.add([1]); Now I check if [1] exists in a : a.has([1]); > false Based on the spec, this might be happening because if type is same for two objects being compared: Return true if x and y refer to the same object. Otherwise, return false. And this also happens: [1] == [1]; > false So it might be that the Set .has() is using == for comparing equality (not sure though). Is there a .contains() method for Set() in JS like Java has? 回答1:

问题 I ran into a problem regarding set in Python 2.7. Here's the appropriate example code block: letters = set(str(raw_input("Type letters: "))) As you can see, the point is to write some letters to assign to "letters" for later use. But if I type "aaabbcdd", the output of "letters" returns set(['a', 'c', 'b', 'd']) My question is how to write the code, so that the output will allow duplicates like this: set(['a','a','a','b','b','c','d','d']) ? 回答1: set doesn't store duplicates, which is why it's

问题 If I have a list of objects, I can use the __cmp__ method to override objects are compared. This affects how the == operator works, and the item in list function. However, it doesn't seem to affect the item in set function - I'm wondering how I can change the MyClass object so that I can override the behaviour how the set compares items. For example, I would like to create an object that returns True in the three print statements at the bottom. At the moment, the last print statement returns

问题 Can anybody know when to use Set and when to use List in hibernate mapping file ? <set name="" table=""> <key> <column name="" /> </key> </set> <list name="" cascade="all"> <key column="" /> <index column="" /> <one-to-many class=""/> </list> Thanks. 回答1: Take a look at this post: @OneToMany List<> vs Set<> difference The main difference is that a list has ordering while a set does not. Also, a set cannot have duplicate values, while a list can. 来源： https://stackoverflow.com/questions/9188718

问题 Guava's ImmutableSet seems to perform quite poorly in my benchmark concerning contains . For some sizes it gets even much slower than List : size benchmark ns linear runtime 100000 ListContains 110279.54 == 100000 SetContains 7.15 = 100000 ImmutableSetContains 76716.47 = 200000 ListContains 275367.66 ===== 200000 SetContains 7.34 = 200000 ImmutableSetContains 322185.50 ====== 500000 ListContains 935210.10 ==================== 500000 SetContains 7.79 = 500000 ImmutableSetContains 1382765.76 ==