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I'm learning c# , and I reached the LinkedList<T> type and I still need to know more, like when should I use it, how do I create one, how do I to use it. I just want information.
If any one knows a good article about this subject, or if you can show me some examples with explanation, such as how to create, how to add and remove, and how to deal with nodes and elements.
Thanks in advance. I really enjoy asking questions around here with all the pros answering and helping.
[EDIT] Changed reference to LinkedList<T> instead of "array linkedlist." I think this was what was meant based on the context.
You can find more information on LinkedList<T> at MSDN, including an example of how to create and use one. Wikipedia has a reasonable article on linked lists, including their history, usage, and some implementation details.
Linked is a collection to store sequences of values of the same type, which is a frequent task, e.g. to represent a queue of cars waiting at a stoplight.
There are many different collection types like linked list, array, map, set etc. Which one to use when depends on their properties, e.g.:
do you need some type of ordering?
is the container associative, storing key-value pairs like a dictionary?
can you store the same element twice?
performance measures - how fast is e.g. inserting, removing, finding an element? This is usually given in Big-O notation, telling you how the time required scales with the number of elements in the collection.
Memory footprint and layout. This also can affect performance, due to good/bad locality.
This collection class implements a doubly linked list. It allows you to quickly determine the immediate sibling for a specified item in the collection. Removing an item from the collection automatically resizes it so that it does not leave any gaps.
For more info on LinkedList class, check out LinkedList at MSDN.
Do you know what a standard Linked List is? It's like one of those (doubly linked) but using .NET Generics to allow you to easily store any Type inside of it.
Honestly, I don't use it, I prefer the more basic List or Dictionary.
For more info on Linked Lists, check out wikipedia. As for generics, there are tons of articles here and at MSDN.
linklist are collections.. they can be use as replacements for arrays.. they can dynamically grow in size and has special helper methods that can help the development or the problem solving be faster.. try to view its methods and properties to understand more.
linklist is a generic collection.. meaning can used to declare type safety declarations..
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I am working on a serialization system using Json, but I need to save events from Buttons (onClick, onHover, etc.) Is there a way about doing this efficiently? (NOTE: The events are all Actions)
Frankly, it is is terrible idea to try to serialize events.
JSON is usually used to serialize data; events are not data - they are implementation details. Most JSON serializers (or more broadly: most serializers) are not interested in delegates / events, because that isn't relevant to data, so: there's a good chance that anything you'd want to do here will need to be manual. Specifically, the problem here is that an event (or rather, the underlying multicast delegate) is effectively zero, one, or multiple pairs of "instance" (optional) and "method" (required).
The method here is a MethodInfo, and there aren't great ways to serialize a MethodInfo as text (although it is at least theoretically possible, although it would be very brittle vs changes to your code.
The instance, however, is an object - and most serializers hate that; in this case, it would combine object (reference) tracking, possibly of objects not otherwise inside the payload, of indeterminate types (so: possibly needing to store type metadata).
Also, deserializing an object model that allows you to point to arbitrary types and methods is a massive security hole, and is a well-known RCE weakness in serializers that (unwisely, IMO) allow this kind of thing (such as BinaryFormatter; for a longer discussion of this topic, see here).
As for what to do instead: whenever an implementation isn't a great fit for a given serializer, the most pragmatic option is to stop fighting the serializer, and work with it instead of against it. For example, it might be that you can create a model that looks kinda like your domain model, but instead of having events/delegates, it might just have a string[] / List<string> that represents the events you need to apply, and your code would worry about how to map between them (mapping methods to strings, and figuring out what the target instance should be, etc). This avoids all of the pain points above, and additionally means that your data is now platform independent, with the payload and the implementation details (your form layout) separate from each-other.
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AsReadOnly() is a convenient method to get a read-only image (not expensive compared to immutable collections' copies) of a collection. I am wondering if ImmutableList has AsReadOnly like method? If no, any easy way to implement similarly?
Immutable collections are inherently read-only. You can easily check in the documentation that ImmutableList<T> already implements IReadOnlyList<T> and IReadOnlyCollection<T> interfaces.
Memory is not allocated when you access elements from immutable collection. On the other hand, when you add an element to some immutable data structure, a new immutable collection is created (and some memory is used). Many immutable collections' implementations do not copy all the data to a new collection but instead share some data from with the old one, so in most cases you should not be too concerned with memory usage/allocation time.
Some collections, e.g. ImmutableHashSet<T>, have a documentation which states that they are optimized in terms of number of memory allocations.
The idea behind sharing some data between immutable collection is not complicated. Wikipedia has an simple example (with a nice diagram) showing how memory can be saved in case of immutable singly-linked lists.
ImmutableList<T> is copied by reference so is perfectly safe to pass around without a performance penalty. Thus there is no need for an AsReadOnly method as it wouldn't make it any easier to copy.
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I'm totally new to programming and I am wondering; when would be a good time
to use an array or an indexer? I want to know what types of applications
would make good use of arrays or indexers. There seems to be other ways of
doing the jobs of the two and less confusing.
The books I read don't provide good examples of situations when I would need
an array or indexer. I don't really need a definition of them as I already
have that. I just need to know what which well known apps have uses for
arrays and indexer?
This is the first time I've ever heard the term "smart array" in C#
No one uses the phrase "smart array" not that I heard of.
http://social.msdn.microsoft.com/Forums/en-US/3b56248f-1ff6-41aa-a0cd-35735e802e13/what-is-indexer-for-in-c
no one calls indexers smart array except the guy in the linked forum post.
indexers used for stuff like Dictionaries and Hashtables
In general I think arrays are a pain to manage, and I don't use them very often. As a programmer, you have to be completely responsible for the length of an array.
string[] str1 = new string[10];
When you add and remove items from the array, you have to be aware of all times where in the array you are.
Personally I avoid arrays when possible and use strongly typed collection, like List
List<string> str1 = new List<string>();
Then I can use the built-in methods to manage the items without having to be as concerned with managing the fine details.
str1.Add("Hello!");
str1.Add("Hello again!");
str1.RemoveAt(0);
Console.WriteLine(str1[0]); //Hello again!
I think answer to why indexer are known as smart array in c#? question is they are not.
Post on MSDN forum does not prove anything. There is nothing about smart array on MSDN documentation. You should follow official feature naming, which is indexer or indexed property. That's the name you can find on
Specification: chapter 10.9 Indexers
An indexer is a member that enables an object to be indexed in the same way as an array. Indexers are declared using indexer-declarations:
Documentation: Indexers (C# Programming Guide)
Indexers allow instances of a class or struct to be indexed just like arrays. Indexers resemble properties except that their accessors take parameters.
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We can use any of these (includes List, ArrayList, Dictionary, Hashtable, Stack, Queue) to hold value or hold reference to other objects as a collection.
But, my question is which one is used when?
Lists
Lists allow duplicate items, can be accessed by index, and support linear traversal.
ArrayList - An array-based list that doesn't support generic types. It does not enforce type safety and should generally be avoided.
List - An array list that supports generic types and enforces type-safety. Since it is non-contiguous, it can grow in size without re-allocating memory for the entire list. This is the more commonly used list collection.
Hashes
Hashes are look-ups in which you give each item in a list a "key" which will be used to retrieve it later. Think of a hash like a table index where you can ask questions like "I'm going to find this object by this string value. Duplicate keys are not allowed.
HashTable - A basic key-value-pair map that functions like an indexed list.
Dictionary - A hashtable that supports generic types and enforces type-safety.
Queues
Queues control how items in a list are accessed. You typically push/pop records from a queue in a particular direction (from either the front or back). Not used for random access in the middle.
Stack - A LIFO (last in, first out) list where you push/pop records on top of each other.
Queue - A FIFO (first in, first out) list where you push records on top and pop them off the bottom.
List can hold duplicate objects
ArrayList is just for compatibility with older versions of the framework where IList didn't exist
Dictionary is used to store pairs of key/value. You cannot have duplicate keys.
Hashtable is basically a List with no possibility of duplicates (and better performance in some scenarios)
Stack stores objects in order they were added (through Push()), and when you retrieve an object (through Pop()) it is removed from the stack in a LIFO manner.
Queue quite similar to a Stack except it is FIFO.
Here are some uses for them.
List: If you just want a list and don't care about any duplicates, i.e list of people, shopping list, list of things to do in life.
Queues: If you want to simulate a queue for example, in a hospital you have a queue and also priority queue (in emergency departments). The triage would determine who is in critical condition and needs to be treated.
Another example is a shopping queue, first person in line is 'usually' the first one to checkout.
Stacks: Used in your internal memory to push and pop values as you pass them to functions/methods.
Another interesting use is, in video game inventory method, where you can pick up an item (push) onto the stack, and drop an item (pop) off the stack.
Hash/Dictionary: These are usually seen used in database, for look up and index.
Depending on what you want to simulate, I do agree with the others, it's handy to read up on data-structures. A book helps but the internet also has a wealth of information.
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I'm writing a service where performance is essential, and I'm not sure what is the fastest thing. I have a few Objects (50-200) which each have an ID in them (ints, e.g. 84397 or 23845). Would it be faster to have a Dictionary, a List of KeyValue Pairs or a List with the indexes set to the IDs with the rest having null values or an array with the same idea?
It depends on which operation you want to execute. Let's assume that you want to find an object with a given ID.
The huge array approach is fastest: Accessing myArray[84397] is a constant-time operation O(1). Of course, this approach requires the most memory.
The dictionary is almost as fast but requires less memory, since it uses a hash table internally.
The list of pairs approach is the slowest, since you might have to traverse the whole list to find your entry, which yields O(n) complexity.
Thus, in your situation, I would choose the dictionary, unless the marginally better performance of the huge array is really relevant in your case.
Dictionary<TKey, TValue> uses a hash table internally so I think it would be the fastest one.
Dictionary versus List Lookup time
Also, for a more detailed explaination of the different collections, check out this question.
You can use Hashtables as well. Dictionary internally using it anyway.
but dictionary has an advantage that it is a GENERIC type which gives you type safety.
here is different thread
Dictionary Vs HashTable
I hope it helps you decide.
Praveen