Multi value Dictionary

Question

How would i create a multi value Dictionary in c    E g  Dictionary lt T T T gt  where the first T is the key and other two are values   so this would be possible  Dictionary lt int object double gt   Thanks

User · Answer

You describe a multimap   You can make the value a List object  to store more than one value   2 for extensibility    Override the dictionary object

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I don t think you can do that directly  You could create a class containing both your object and double and put an instance of it in the dictionary though   class Pair       object obj      double dbl     Dictionary lt int  Pair gt    new Dictionary lt int  Pair gt

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If the values are related  why not encapsulate them in a class and just use the plain old Dictionary

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Dictionary lt T1  Tuple lt T2  T3 gt  gt    Edit  Sorry - I forgot you don t get Tuples until  NET 4 0 comes out  D oh

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I think this is quite overkill for a dictionary semantics  since dictionary is by definition is a collection of keys and its respective values  just like the way we see a book of language dictionary that contains a word as the key and its descriptive meaning as the value   But you can represent a dictionary that can contain collection of values  for example   Dictionary lt String List lt Customer gt  gt    Or a dictionary of a key and the value as a dictionary   Dictionary lt Customer Dictionary lt Order OrderDetail gt  gt    Then you ll have a dictionary that can have multiple values

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Just create a Pair lt TFirst  TSecond gt  type and use that as your value   I have an example of one in my C  in Depth source code  Reproduced here for simplicity   using System  using System Collections Generic   public sealed class Pair lt TFirst  TSecond gt        IEquatable lt Pair lt TFirst  TSecond gt  gt        private readonly TFirst first      private readonly TSecond second       public Pair TFirst first  TSecond second                this first   first          this second   second             public TFirst First               get   return first               public TSecond Second               get   return second               public bool Equals Pair lt TFirst  TSecond gt  other                if  other    null                        return false                    return EqualityComparer lt TFirst gt  Default Equals this First  other First   amp  amp                 EqualityComparer lt TSecond gt  Default Equals this Second  other Second              public override bool Equals object o                return Equals o as Pair lt TFirst  TSecond gt               public override int GetHashCode                 return EqualityComparer lt TFirst gt  Default GetHashCode first    37                  EqualityComparer lt TSecond gt  Default GetHashCode second

User · Answer

If you are trying to group values together this may be a great opportunity to create a simple struct or class and use that as the value in a dictionary   public struct MyValue       public object Value1      public double Value2      then you could have your dictionary  var dict   new Dictionary lt int  MyValue gt       you could even go a step further and implement your own dictionary class that will handle any special operations that you would need  for example if you wanted to have an Add method that accepted an int  object  and double  public class MyDictionary   Dictionary lt int  MyValue gt        public void Add int key  object value1  double value2                MyValue val          val Value1   value1          val Value2   value2          this Add key  val             then you could simply instantiate and add to the dictionary like so and you wouldn t have to worry about creating  MyValue  structs   var dict   new MyDictionary    dict Add 1  new Object    2 22

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I solved Using   Dictionary lt short  string   gt    Like this  Dictionary lt short  string   gt  result   new Dictionary lt short  string   gt     result Add 1             new string                                                FirstString                        Second                                                     return result

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I know this is an old thread  but - since it s not been mentioned this works    Dictionary lt string  object gt  LookUp   new Dictionary lt string  object gt       LookUp Add  bob   new   age    23   height    2 1m   weight    110kg       LookUp Add  jasper   new   age    33   height    1 75m   weight    90kg       foreach KeyValuePair lt string  object gt  entry in LookUp             object person   entry Value        Console WriteLine  Person name     entry Key     Age       person age

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Here is an implementation of a single key to multi value map in C  which uses a set based key type   https   github com ColmBhandal CsharpExtras blob master CsharpExtras Dictionary MultiValueMapImpl cs  The dictionary behaves like a regular dictionary from the key type onto a set of the value type  but also provides functionality to directly add a single value of the value type  and in the background handles the creation of an underlying set and or addition to that set

[c#] Multi value Dictionary

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