I have to modify the following code. I have given a list of tasks (httpClient.Run method returns Task). I have to run them and wait until all of them are done. Later on I need to collect all results and build response.
var tasks = new Dictionary<string, Task<string>>();
tasks.Add("CODE1", service.RunTask("CODE1"));
tasks.Add("CODE2", service.RunTask("CODE2"));
tasks.Add("CODE3", service.RunTask("CODE3"));
//...
var result = await Task.WhenAll(tasks.Values); // how to get CODE (dictionary KEY) here
// build response
The problem above is that when we get results we have lost exactly which task was run. results is string array, but I need, for instance,KeyValuePair array. We need to know which task (CODE) was run, so that we can build result properly.
You can use async in a Select lambda to transform the KeyValuePair<T1, Task<T2>s into Task<KeyValuePair<T1, T2>>s.
var resultTasks = tasks.Select(async pair => KeyValuePair.Create(pair.Key, await pair.Value));
IReadOnlyCollection<KeyValuePair<string, string>> results = await Task.WhenAll(resultTasks);
Something like this ought to do it. This is written assuming you do the Task.WhenAll() call first. Otherwise, you'll block the thread when you start to enumerate over resultsWithKeys.
await Task.WhenAll(tasks.Values());
var resultsWithKeys = tasks.Select(
x => new
{
Key = x.Key,
Result = x.Value.Result
});
foreach (var result in resultsWithKeys)
Console.WriteLine($"{result.Key} - {result.Result.SomeValue}");
The Dictionary<string, Task<string>> contains tasks that do not propagate the key as part of their Result. If you prefer to have tasks that include the key in their result, you'll have to create a new dictionary and fill it with new tasks that wrap the existing tasks. The TResult of these new tasks can be a struct of your choice, for example a KeyValuePair<string, string>. Below is an extension method WithKeys that allows to create easily the new dictionary with the new tasks:
public static Dictionary<TKey, Task<KeyValuePair<TKey, TValue>>> WithKeys<TKey, TValue>(
this Dictionary<TKey, Task<TValue>> source)
{
return source.ToDictionary(e => e.Key,
async e => KeyValuePair.Create(e.Key, await e.Value.ConfigureAwait(false)),
source.Comparer);
}
Usage example:
KeyValuePair<string, string>[] result = await Task.WhenAll(tasks.WithKeys().Values);
I have a ConcurrentDictionary that has as key a long and as value a hashset of int. I want that if the key isn't in the dictionary, add a new hashset with the first element. If the key exists, add the new element to the existing dictionary.
I am trying something like that:
ConcurrentDictionary<long, HashSet<int>> myDic = new ConcurrentDictionary<long, HashSet<int>>();
int myElement = 1;
myDic.AddOrUpdate(1, new Hashset<int>(){myFirstElement},
(key, actualValue) => actualValue.Add(myElement));
The problem with this code is the third parameter, because .Add() method returns a bool and the AddOrUpdate expects a hashset. The first and second parameters are right.
So my question is how I can add a new element to the hashset in thread-safe way and avoid duplicates (it is the reason why I am using a hashset as value). The problem of the hashset is that it is not thread-safe and if I get it first and later add the new element, I am doing outside of the dictionary and I could have problems.
Thanks.
To fix compiler error you can do this:
myDic.AddOrUpdate(1, new HashSet<int>() { myFirstElement },
(key, actualValue) => {
actualValue.Add(myFirstElement);
return actualValue;
});
BUT this is not thread safe, because "update" function is not run inside any lock so you are potentially adding to not-thread-safe HashSet from multiple threads. This might result in (for example) losing values (so you were adding 1000 items to HashSet but in the end you have only 970 items in it for example). Update function in AddOrUpdate should not have any side effects and here it does.
You can lock yourself over adding values to HashSet:
myDic.AddOrUpdate(1, new HashSet<int>() { myFirstElement },
(key, actualValue) => {
lock (actualValue) {
actualValue.Add(myFirstElement);
return actualValue;
}
});
But then question is why you are using lock-free structure (ConcurrentDictionary) in the first place. Besides that - any other code might get HashSet from your dictionary and add value there without any locks, making the whole thing useless. So if you decide to go that way for some reason - you have to ensure that all code locks when accessing HashSet from that dictionary.
Instead of all that - just use concurrent collection instead of HashSet. There is no ConcurrentHashSet as far as I know but you can use another ConcurrentDictionary with dummy keys as a replacement (or look over internet for custom implementations).
Side note. Here
myDic.AddOrUpdate(1, new Hashset<int>(){myFirstElement},
you create new HashSet every time when calling AddOrUpdate, even if that dictionary is not needed because key is already there. Instead use overload with add value factory:
myDic.AddOrUpdate(1, (key) => new HashSet<int>() { myFirstElement },
Edit: sample usage of ConcurrentDictionary as hash set:
var myDic = new ConcurrentDictionary<long, ConcurrentDictionary<int, byte>>();
long key = 1;
int element = 1;
var hashSet = myDic.AddOrUpdate(key,
_ => new ConcurrentDictionary<int, byte>(new[] {new KeyValuePair<int, byte>(element, 0)}),
(_, oldValue) => {
oldValue.TryAdd(element, 0);
return oldValue;
});
If you wrap the anonymous function definition in curly braces, you can define multiple statements in the body of the function and thus specify the return value like this:
myDic.AddOrUpdate(1, new HashSet<int>() { myFirstElement },
(key, actualValue) => {
actualValue.Add(myElement);
return actualValue;
});
I want to build an Dictonary like this :
Dictionary<String, ArrayList> myDic = new Dictionary<String, ArrayList>();
in the end i want a structure like :
["blabla"] => array(1,2,3)
["foo"] => array(1,4,6,8)
.......
to build this i run in a loop and in every loop build some strings ,
first question :
how to check every time if this string exists
in the dictionary , if its not exists open a new entry in dictionary with one element in the array list, if exists only add another element to the array list
and another question:
how can i sort this dictionary according to number of elements in the array list(In descending order) like :
["foo"] => array(1,4,6,2,8)
["bar"] => array(4,6,2,8)
["bla"] => array(1,2,3)
["blo"] => array(1,2)
.......
thanks !
Use the right tool for the job. The data structure you want is called a "multi-dictionary" - that is a dictionary that maps from a key to a sequence of values, rather than from a key to a unique value.
The PowerCollections codebase contains an implementation of MultiDictionary that probably does what you want. I would use it rather than writing your own.
To sort the dictionary into a sequence of key/sequence pairs ordered by the length of the sequence, I would use a LINQ query with an "order by" clause. That seems like the easiest way to do it.
Instead of ArrayList you should use an array or List<T>. Assuming you have a Dictionary<string, int> called source this should work:
var items = source
.GroupBy(kvp => kvp.Key)
.Select(grp => new { Key = grp.Key, Items = grp.Select(kvp => kvp.Value).ToArray() })
.OrderByDescending(i => i.Items.Length);
To explain, Dictionary<TKey, TValue> implements IEnumerable<KeyValuePair<TKey, TValue>> so can be considered a sequence of key-value pairs. Group by groups the pairs by key and then Select creates a sequence of an anonymous type which contains the key and associated values in a Key and Items property respectively. This sequence is then ordered by the number of items in the Items array of each object.
If you want to order them by the length of the created array, you can't use a dictionary since they are not ordered.
To check if a key exists in a dictionary and use the value if it does, you can use TryGetValue:
ArrayList array;
if(!myDic.TryGetValue("blabla", out array))
{
array = new ArrayList();
myDic["blabla"] = array;
}
array.Add(42);
Would something like this work:
if (myDic.ContainsKey(myString))
myDic[myString].Add(myNumber);
else
myDic.Add(myString, new ArrayList(new int[] {myNumber}));
I often have to sort a dictionary (consisting of keys & values) by value. For example, I have a hash of words and respective frequencies that I want to order by frequency.
There is a SortedList which is good for a single value (say frequency), that I want to map back to the word.
SortedDictionary orders by key, not value. Some resort to a custom class, but is there a cleaner way?
Use LINQ:
Dictionary<string, int> myDict = new Dictionary<string, int>();
myDict.Add("one", 1);
myDict.Add("four", 4);
myDict.Add("two", 2);
myDict.Add("three", 3);
var sortedDict = from entry in myDict orderby entry.Value ascending select entry;
This would also allow for great flexibility in that you can select the top 10, 20 10%, etc. Or if you are using your word frequency index for type-ahead, you could also include StartsWith clause as well.
Use:
using System.Linq.Enumerable;
...
List<KeyValuePair<string, string>> myList = aDictionary.ToList();
myList.Sort(
delegate(KeyValuePair<string, string> pair1,
KeyValuePair<string, string> pair2)
{
return pair1.Value.CompareTo(pair2.Value);
}
);
Since you're targeting .NET 2.0 or above, you can simplify this into lambda syntax -- it's equivalent, but shorter. If you're targeting .NET 2.0 you can only use this syntax if you're using the compiler from Visual Studio 2008 (or above).
var myList = aDictionary.ToList();
myList.Sort((pair1,pair2) => pair1.Value.CompareTo(pair2.Value));
You could use:
var ordered = dict.OrderBy(x => x.Value).ToDictionary(x => x.Key, x => x.Value);
You can sort a Dictionary by value and save it back to itself (so that when you foreach over it the values come out in order):
dict = dict.OrderBy(x => x.Value).ToDictionary(x => x.Key, x => x.Value);
Sure, it may not be correct, but it works. Hyrum's Law means that this will very likely continue to work.
Looking around, and using some C# 3.0 features we can do this:
foreach (KeyValuePair<string,int> item in keywordCounts.OrderBy(key=> key.Value))
{
// do something with item.Key and item.Value
}
This is the cleanest way I've seen and is similar to the Ruby way of handling hashes.
On a high level, you have no other choice than to walk through the whole Dictionary and look at each value.
Maybe this helps:
http://bytes.com/forum/thread563638.html
Copy/Pasting from John Timney:
Dictionary<string, string> s = new Dictionary<string, string>();
s.Add("1", "a Item");
s.Add("2", "c Item");
s.Add("3", "b Item");
List<KeyValuePair<string, string>> myList = new List<KeyValuePair<string, string>>(s);
myList.Sort(
delegate(KeyValuePair<string, string> firstPair,
KeyValuePair<string, string> nextPair)
{
return firstPair.Value.CompareTo(nextPair.Value);
}
);
You'd never be able to sort a dictionary anyway. They are not actually ordered. The guarantees for a dictionary are that the key and value collections are iterable, and values can be retrieved by index or key, but there is no guarantee of any particular order. Hence you would need to get the name value pair into a list.
You do not sort entries in the Dictionary. Dictionary class in .NET is implemented as a hashtable - this data structure is not sortable by definition.
If you need to be able to iterate over your collection (by key) - you need to use SortedDictionary, which is implemented as a Binary Search Tree.
In your case, however the source structure is irrelevant, because it is sorted by a different field. You would still need to sort it by frequency and put it in a new collection sorted by the relevant field (frequency). So in this collection the frequencies are keys and words are values. Since many words can have the same frequency (and you are going to use it as a key) you cannot use neither Dictionary nor SortedDictionary (they require unique keys). This leaves you with a SortedList.
I don't understand why you insist on maintaining a link to the original item in your main/first dictionary.
If the objects in your collection had a more complex structure (more fields) and you needed to be able to efficiently access/sort them using several different fields as keys - You would probably need a custom data structure that would consist of the main storage that supports O(1) insertion and removal (LinkedList) and several indexing structures - Dictionaries/SortedDictionaries/SortedLists. These indexes would use one of the fields from your complex class as a key and a pointer/reference to the LinkedListNode in the LinkedList as a value.
You would need to coordinate insertions and removals to keep your indexes in sync with the main collection (LinkedList) and removals would be pretty expensive I'd think.
This is similar to how database indexes work - they are fantastic for lookups but they become a burden when you need to perform many insetions and deletions.
All of the above is only justified if you are going to do some look-up heavy processing. If you only need to output them once sorted by frequency then you could just produce a list of (anonymous) tuples:
var dict = new SortedDictionary<string, int>();
// ToDo: populate dict
var output = dict.OrderBy(e => e.Value).Select(e => new {frequency = e.Value, word = e.Key}).ToList();
foreach (var entry in output)
{
Console.WriteLine("frequency:{0}, word: {1}",entry.frequency,entry.word);
}
You could use:
Dictionary<string, string> dic= new Dictionary<string, string>();
var ordered = dic.OrderBy(x => x.Value);
return ordered.ToDictionary(t => t.Key, t => t.Value);
Or for fun you could use some LINQ extension goodness:
var dictionary = new Dictionary<string, int> { { "c", 3 }, { "a", 1 }, { "b", 2 } };
dictionary.OrderBy(x => x.Value)
.ForEach(x => Console.WriteLine("{0}={1}", x.Key,x.Value));
Sorting a SortedDictionary list to bind into a ListView control using VB.NET:
Dim MyDictionary As SortedDictionary(Of String, MyDictionaryEntry)
MyDictionaryListView.ItemsSource = MyDictionary.Values.OrderByDescending(Function(entry) entry.MyValue)
Public Class MyDictionaryEntry ' Need Property for GridViewColumn DisplayMemberBinding
Public Property MyString As String
Public Property MyValue As Integer
End Class
XAML:
<ListView Name="MyDictionaryListView">
<ListView.View>
<GridView>
<GridViewColumn DisplayMemberBinding="{Binding Path=MyString}" Header="MyStringColumnName"></GridViewColumn>
<GridViewColumn DisplayMemberBinding="{Binding Path=MyValue}" Header="MyValueColumnName"></GridViewColumn>
</GridView>
</ListView.View>
</ListView>
The other answers are good, if all you want is to have a "temporary" list sorted by Value. However, if you want to have a dictionary sorted by Key that automatically synchronizes with another dictionary that is sorted by Value, you could use the Bijection<K1, K2> class.
Bijection<K1, K2> allows you to initialize the collection with two existing dictionaries, so if you want one of them to be unsorted, and you want the other one to be sorted, you could create your bijection with code like
var dict = new Bijection<Key, Value>(new Dictionary<Key,Value>(),
new SortedDictionary<Value,Key>());
You can use dict like any normal dictionary (it implements IDictionary<K, V>), and then call dict.Inverse to get the "inverse" dictionary which is sorted by Value.
Bijection<K1, K2> is part of Loyc.Collections.dll, but if you want, you could simply copy the source code into your own project.
Note: In case there are multiple keys with the same value, you can't use Bijection, but you could manually synchronize between an ordinary Dictionary<Key,Value> and a BMultiMap<Value,Key>.
Actually in C#, dictionaries don't have sort() methods.
As you are more interested in sort by values,
you can't get values until you provide them key.
In short, you need to iterate through them using LINQ's OrderBy(),
var items = new Dictionary<string, int>();
items.Add("cat", 0);
items.Add("dog", 20);
items.Add("bear", 100);
items.Add("lion", 50);
// Call OrderBy() method here on each item and provide them the IDs.
foreach (var item in items.OrderBy(k => k.Key))
{
Console.WriteLine(item);// items are in sorted order
}
You can do one trick:
var sortedDictByOrder = items.OrderBy(v => v.Value);
or:
var sortedKeys = from pair in dictName
orderby pair.Value ascending
select pair;
It also depends on what kind of values you are storing: single (like string, int) or multiple (like List, Array, user defined class).
If it's single you can make list of it and then apply sort.
If it's user defined class, then that class must implement IComparable, ClassName: IComparable<ClassName> and override compareTo(ClassName c) as they are more faster and more object oriented than LINQ.
Required namespace : using System.Linq;
Dictionary<string, int> counts = new Dictionary<string, int>();
counts.Add("one", 1);
counts.Add("four", 4);
counts.Add("two", 2);
counts.Add("three", 3);
Order by desc :
foreach (KeyValuePair<string, int> kvp in counts.OrderByDescending(key => key.Value))
{
// some processing logic for each item if you want.
}
Order by Asc :
foreach (KeyValuePair<string, int> kvp in counts.OrderBy(key => key.Value))
{
// some processing logic for each item if you want.
}
Suppose we have a dictionary as:
Dictionary<int, int> dict = new Dictionary<int, int>();
dict.Add(21,1041);
dict.Add(213, 1021);
dict.Add(45, 1081);
dict.Add(54, 1091);
dict.Add(3425, 1061);
dict.Add(768, 1011);
You can use temporary dictionary to store values as:
Dictionary<int, int> dctTemp = new Dictionary<int, int>();
foreach (KeyValuePair<int, int> pair in dict.OrderBy(key => key.Value))
{
dctTemp.Add(pair.Key, pair.Value);
}
The easiest way to get a sorted Dictionary is to use the built in SortedDictionary class:
//Sorts sections according to the key value stored on "sections" unsorted dictionary, which is passed as a constructor argument
System.Collections.Generic.SortedDictionary<int, string> sortedSections = null;
if (sections != null)
{
sortedSections = new SortedDictionary<int, string>(sections);
}
sortedSections will contain the sorted version of sections
Sort and print:
var items = from pair in players_Dic
orderby pair.Value descending
select pair;
// Display results.
foreach (KeyValuePair<string, int> pair in items)
{
Debug.Log(pair.Key + " - " + pair.Value);
}
Change descending to acending to change sort order
A dictionary by definition is an unordered associative structure that contains only values and keys in a hashable way. In other words has not a previsible way to orderer a dictionary.
For reference read this article from python language.
Link
python data structures
Best way:
var list = dict.Values.OrderByDescending(x => x).ToList();
var sortedData = dict.OrderBy(x => list.IndexOf(x.Value));
The following code snippet sorts a Dictionary by values.
The code first creates a dictionary and then uses OrderBy method to sort the items.
public void SortDictionary()
{
// Create a dictionary with string key and Int16 value pair
Dictionary<string, Int16> AuthorList = new Dictionary<string, Int16>();
AuthorList.Add("Mahesh Chand", 35);
AuthorList.Add("Mike Gold", 25);
AuthorList.Add("Praveen Kumar", 29);
AuthorList.Add("Raj Beniwal", 21);
AuthorList.Add("Dinesh Beniwal", 84);
// Sorted by Value
Console.WriteLine("Sorted by Value");
Console.WriteLine("=============");
foreach (KeyValuePair<string, Int16> author in AuthorList.OrderBy(key => key.Value))
{
Console.WriteLine("Key: {0}, Value: {1}", author.Key, author.Value);
}
}
You can sort the Dictionary by value and get the result in dictionary using the code below:
Dictionary <<string, string>> ShareUserNewCopy =
ShareUserCopy.OrderBy(x => x.Value).ToDictionary(pair => pair.Key,
pair => pair.Value);
Given you have a dictionary you can sort them directly on values using below one liner:
var x = (from c in dict orderby c.Value.Order ascending select c).ToDictionary(c => c.Key, c=>c.Value);