How do you sort a dictionary by value

Question

I often have to sort a dictionary  consisting of keys  amp  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 it back to the word   SortedDictionary orders by key  not value  Some resort to a custom class  but is there a cleaner way

User · Answer

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

User · Answer

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

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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 lt K1  K2 gt  class   Bijection lt K1  K2 gt  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 lt Key  Value gt  new Dictionary lt Key Value gt                                     new SortedDictionary lt Value Key gt        You can use dict like any normal dictionary  it implements IDictionary lt K  V gt    and then call dict Inverse to get the  inverse  dictionary which is sorted by Value   Bijection lt K1  K2 gt  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 lt Key Value gt  and a BMultiMap lt Value Key gt

User · Answer

Looking around  and using some C  3 0 features we can do this   foreach  KeyValuePair lt string int gt  item in keywordCounts OrderBy key  gt  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

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Required namespace   using System Linq   Dictionary lt string  int gt  counts   new Dictionary lt string  int gt     counts Add  one   1   counts Add  four   4   counts Add  two   2   counts Add  three   3     Order by desc    foreach  KeyValuePair lt string  int gt  kvp in counts OrderByDescending key   gt  key Value        some processing logic for each item if you want      Order by Asc    foreach  KeyValuePair lt string  int gt  kvp in counts OrderBy key   gt  key Value        some processing logic for each item if you want

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Or for fun you could use some LINQ extension goodness   var dictionary   new Dictionary lt string  int gt       c   3       a   1       b   2      dictionary OrderBy x   gt  x Value     ForEach x   gt  Console WriteLine   0   1    x Key x Value

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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   gt  x Value  ToDictionary x   gt  x Key  x   gt  x Value     Sure  it may not be correct  but it works

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Use LINQ   Dictionary lt string  int gt  myDict   new Dictionary lt string  int gt     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

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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   gt  c Key  c  gt c Value

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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 lt string  int gt        ToDo  populate dict  var output   dict OrderBy e   gt  e Value  Select e   gt  new  frequency   e Value  word   e Key   ToList     foreach  var entry in output        Console WriteLine  frequency  0   word   1   entry frequency entry word

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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 lt string  string gt  s   new Dictionary lt string  string gt     s Add  1    a Item    s Add  2    c Item    s Add  3    b Item     List lt KeyValuePair lt string  string gt  gt  myList   new List lt KeyValuePair lt string  string gt  gt  s   myList Sort      delegate KeyValuePair lt string  string gt  firstPair      KeyValuePair lt string  string gt  nextPair                return firstPair Value CompareTo nextPair Value

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var ordered   dict OrderBy x   gt  x Value  ToDictionary x   gt  x Key  x   gt  x Value

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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 lt string  int gt     items Add  quot cat quot   0   items Add  quot dog quot   20   items Add  quot bear quot   100   items Add  quot lion quot   50       Call OrderBy   method here on each item and provide them the IDs  foreach  var item in items OrderBy k   gt  k Key         Console WriteLine item     items are in sorted order    You can do one trick  var sortedDictByOrder   items OrderBy v   gt  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 lt ClassName gt  and override compareTo ClassName c  as they are more faster and more object oriented than LINQ

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Suppose we have a dictionary as      Dictionary lt int  int gt  dict   new Dictionary lt int  int gt        dict Add 21 1041      dict Add 213  1021      dict Add 45  1081      dict Add 54  1091      dict Add 3425  1061      sict Add 768  1011     1  you can use temporary dictionary to store values as            Dictionary lt int  int gt  dctTemp   new Dictionary lt int  int gt              foreach  KeyValuePair lt int  int gt  pair in dict OrderBy key   gt  key Value                         dctTemp  Add pair Key  pair Value

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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    lt ListView Name  MyDictionaryListView  gt       lt ListView View gt           lt GridView gt               lt GridViewColumn DisplayMemberBinding   Binding Path MyString   Header  MyStringColumnName  gt  lt  GridViewColumn gt               lt GridViewColumn DisplayMemberBinding   Binding Path MyValue   Header  MyValueColumnName  gt  lt  GridViewColumn gt            lt  GridView gt       lt  ListView View gt   lt  ListView gt

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Use   using System Linq Enumerable      List lt KeyValuePair lt string  string gt  gt  myList   aDictionary ToList     myList Sort      delegate KeyValuePair lt string  string gt  pair1      KeyValuePair lt string  string gt  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 nbsp Studio nbsp 2008  or above    var myList   aDictionary ToList     myList Sort  pair1 pair2    gt  pair1 Value CompareTo pair2 Value

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Sort and print  var items   from pair in players Dic                 orderby pair Value descending                 select pair      Display results  foreach  KeyValuePair lt string  int gt  pair in items        Debug Log pair Key    quot  -  quot    pair Value      Change descending to acending to change sort order

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Dictionary lt string  string gt  dic  new Dictionary lt string  string gt     var ordered   dic OrderBy x   gt  x Value   return ordered ToDictionary t   gt  t Key  t   gt  t Value

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You can sort the Dictionary by value and get the result in dictionary using the code below   Dictionary  lt  lt string  string gt  gt  ShareUserNewCopy           ShareUserCopy OrderBy x   gt  x Value  ToDictionary pair   gt  pair Key                                                          pair   gt  pair Value

[c#] How do you sort a dictionary by value?

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