collections

问题 I have some code with Map<String, Map<String, String>> objects, which works (it is instantiated as a HashMap of HashMaps), but I wonder whether there is a better way to represent this data structure in Guava. I have considered Multimap , but while there is ListMultimap and SetMultimap in Guava, I have found no "MapMultimap". I have also checked Table, which seems to be more like it, but its name is making me uncomfortable: what I have is definitely not a table but a tree. (There is no overlap

问题 In a (max) heap it is easy to find the biggest item in O(1) time, but to actually remove it you need complexity of O(log(n)) . So if the insertion and deletion from a heap is both O(log(n)) , what are the advantages of a heap over binary tree for representing a priority queue? 回答1: Heaps use less memory. They can be implemented as arrays and thus there is no overhead for storing pointers. (A binary tree CAN be implemented as an array, but there is likely to be many empty "gaps" which could

问题 I have two ObservableCollection lists, that i want to unite. My naive approach was to use the Union - Method: ObservableCollection<Point> unitedPoints = observableCollection1.Union(observableCollection2); ObservableCollection1/2 are of type ObservableCollection too. But the Compiler throws the following error for this line: The Type "System.Collections.Generic.IEnumerable" can't be converted implicit to "System.Collections.ObjectModel.ObservableCollection". An explicite conversion already

问题 I'm using the Laravel contains method on a collection https://laravel.com/docs/5.3/collections#method-contains. But it does not work for me. foreach ($this->options as $option) { if($options->contains($option->id)) { dd('test'); } } dd($options); looks like this: Collection {#390 #items: array:1 [ 0 => array:3 [ 0 => array:7 [ "id" => 10 "slug" => "test" "name" => "test" "poll_id" => 4 "created_at" => "2016-11-12 20:42:42" "updated_at" => "2016-11-12 20:42:42" "votes" => [] ] 1 => array:7 [

问题 I'm using the Laravel contains method on a collection https://laravel.com/docs/5.3/collections#method-contains. But it does not work for me. foreach ($this->options as $option) { if($options->contains($option->id)) { dd('test'); } } dd($options); looks like this: Collection {#390 #items: array:1 [ 0 => array:3 [ 0 => array:7 [ "id" => 10 "slug" => "test" "name" => "test" "poll_id" => 4 "created_at" => "2016-11-12 20:42:42" "updated_at" => "2016-11-12 20:42:42" "votes" => [] ] 1 => array:7 [

问题 If I have a rarely used collection in some class which may be instantiated many times, I may sometimes resort to the following "idiom" in order to save unnecessary object creations: List<Object> list = null; void add(Object object) { if (list == null) list = new ArrayList<Object>(); list.add(object); } // somewhere else if (list != null) for (Object object : list) ; Now I was wondering if I couldn't eliminate those null checks using Collections.emptyList() , however then I would have to alter

问题 I am trying to join a custom collection with products to show the product name (not just the id) in the admin grid widget. So far i can't find the correct syntax. I am able to retrieve the products with the product name by the following: Mage::getModel('catalog/product')->getCollection()->addAttributeToSelect('name'); and i can retrieve my custom collection with: Mage::getResourceModel('xyz_mymodule/model_collection'); How do i join the two so that the module collection is the primary

问题 I am trying to join a custom collection with products to show the product name (not just the id) in the admin grid widget. So far i can't find the correct syntax. I am able to retrieve the products with the product name by the following: Mage::getModel('catalog/product')->getCollection()->addAttributeToSelect('name'); and i can retrieve my custom collection with: Mage::getResourceModel('xyz_mymodule/model_collection'); How do i join the two so that the module collection is the primary

问题 As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, visit the help center for guidance. Closed 7 years ago . What are your favorite code snippets with ruby collections? Preferably they should be discovery for you, be expressive, readable and

问题 I have an object "person" with several collections ("documents", "contacts", "etc"). I would like to save "person" and automatically the collection too. This is my controller: $em = $this->getDoctrine()->getManager(); $persona = new Persona(); $formulario = $this->createForm( PersonaType::class, $persona, array('action' => $this->generateUrl('persona_create'), 'method' => 'POST') ); $formulario->handleRequest($request); $em->persist($persona); $em->flush(); When I dump "$persona", I have the