Multi-key dictionary in c

Question

I know there isn t one in the BCL but can anyone point me to a good opensource one   By Multi I mean 2 keys   -

User · Answer

I use a Tuple as the keys in a Dictionary   public class Tuple lt T1  T2 gt        public T1 Item1   get  private set        public T2 Item2   get  private set            implementation details     Be sure to override Equals and GetHashCode and define operator   and operator   as appropriate  You can expand the Tuple to hold more items as needed   NET 4 0 will include a built-in Tuple

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I think you would need a Tuple2 like class   Be sure that it s GetHashCode   and Equals   is based upon the two contained elements   See Tuples in C

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I m currently simply concatenating the keys into a single string as a workaround  Of course  this will not work on non-string keys  Would love to know the answer as well

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I frequently use this because it s short and provides the syntactic sugar I need     public class MultiKeyDictionary lt T1  T2  T3 gt    Dictionary lt T1  Dictionary lt T2  T3 gt  gt        new public Dictionary lt T2  T3 gt  this T1 key                get                       if   ContainsKey key                   Add key  new Dictionary lt T2  T3 gt                   Dictionary lt T2  T3 gt  returnObj              TryGetValue key  out returnObj                return returnObj                      To use it   dict cat  fish    9000    where the  Cat  key doesn t have to exist either

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If anyone is looking for a ToMultiKeyDictionary   here is an implementation that should work with most of the answers here  based on Herman s    public static class Extensions MultiKeyDictionary        public static MultiKeyDictionary lt K1  K2  V gt  ToMultiKeyDictionary lt S  K1  K2  V gt  this IEnumerable lt S gt  items  Func lt S  K1 gt  key1  Func lt S  K2 gt  key2  Func lt S  V gt  value            var dict   new MultiKeyDictionary lt K1  K2  V gt              foreach  S i in items                 dict Add key1 i   key2 i   value i                        return dict              public static MultiKeyDictionary lt K1  K2  K3  V gt  ToMultiKeyDictionary lt S  K1  K2  K3  V gt  this IEnumerable lt S gt  items  Func lt S  K1 gt  key1  Func lt S  K2 gt  key2  Func lt S  K3 gt  key3  Func lt S  V gt  value            var dict   new MultiKeyDictionary lt K1  K2  K3  V gt              foreach  S i in items                 dict Add key1 i   key2 i   key3 i   value i                        return dict

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Here s my implementation   I wanted something to hide the implementation of the Tuple concept     public class TwoKeyDictionary lt TKey1  TKey2  TValue gt    Dictionary lt TwoKey lt TKey1  TKey2 gt   TValue gt          public static TwoKey lt TKey1  TKey2 gt  Key TKey1 key1  TKey2 key2              return new TwoKey lt TKey1  TKey2 gt  key1  key2              public TValue this TKey1 key1  TKey2 key2              get   return this Key key1  key2            set   this Key key1  key2     value               public void Add TKey1 key1  TKey2 key2  TValue value              Add Key key1  key2   value              public bool ContainsKey TKey1 key1  TKey2 key2              return ContainsKey Key key1  key2                 public class TwoKey lt TKey1  TKey2 gt    Tuple lt TKey1  TKey2 gt          public TwoKey TKey1 item1  TKey2 item2    base item1  item2           public override string ToString               return string Format    0   1     Item1  Item2               It helps keeps the usage looking like a Dictionary  item Add 1   D   5 6    value   item 1   D

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Here s another example using the Tuple class with the Dictionary              Setup Dictionary     Dictionary lt Tuple lt string  string gt   string gt  testDictionary   new Dictionary lt Tuple lt string  string gt   string gt                 new Tuple lt string  string gt   key1   key2     value1             new Tuple lt string  string gt   key1   key3     value2             new Tuple lt string  string gt   key2   key3     value3                Query Dictionary     public string FindValue string stuff1  string stuff2                return testDictionary Tuple Create stuff1  stuff2

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I ve googled for this one  http   www codeproject com KB recipes multikey-dictionary aspx  I guess it s main feature compared to using struct to contain 2 keys in regular dictionary is that you can later reference by one of the keys  instead of having to supply 2 keys

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Could you use a Dictionary lt TKey1 Dictionary lt TKey2 TValue gt  gt    You could even subclass this   public class DualKeyDictionary lt TKey1 TKey2 TValue gt    Dictionary lt TKey1 Dictionary lt TKey2 TValue gt  gt    EDIT  This is now a duplicate answer  It also is limited in its practicality  While it does  work  and provide ability to code dict key1  key2   there are lots of  workarounds  to get it to  just work    HOWEVER  Just for kicks  one could implement Dictionary nonetheless  but at this point it gets a little verbose   public class DualKeyDictionary lt TKey1  TKey2  TValue gt    Dictionary lt TKey1  Dictionary lt TKey2  TValue gt  gt    IDictionary lt  object    TValue  gt         region IDictionary lt object   TValue gt  Members      void IDictionary lt object    TValue gt  Add  object   key  TValue value                 if   key    null    key Length    2               throw new ArgumentException   Invalid Key              TKey1 key1   key 0  as TKey1          TKey2 key2   key 1  as TKey2           if    ContainsKey  key1                 Add  key1  new Dictionary lt TKey2  TValue gt                this key1  key2    value             bool IDictionary lt object    TValue gt  ContainsKey  object   key                 if   key    null    key Length    2               throw new ArgumentException   Invalid Key              TKey1 key1   key 0  as TKey1          TKey2 key2   key 1  as TKey2           if    ContainsKey  key1                 return false           if    this key1  ContainsKey  key2                 return false           return true

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Take a look at Wintellect s PowerCollections  CodePlex download   I think their MultiDictionary does something like that    It s a dictionary of dictionaries  so you have 2 keys to access each object  the key for the main dictionary to get you the required sub dictionary  and then the second key for the sub dictionary to get you the required item  Is that what you mean

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Here s a fleshed out example of a pair class which can be used as the key to a Dictionary   public class Pair lt T1  T2 gt        public T1 Left   get  private set        public T2 Right   get  private set         public Pair T1 t1  T2 t2                Left   t1          Right   t2             public override bool Equals object obj                if  ReferenceEquals null  obj   return false          if  ReferenceEquals this  obj   return true          if  obj GetType      typeof Pair lt T1  T2 gt    return false          return Equals  Pair lt T1  T2 gt  obj              public bool Equals Pair lt T1  T2 gt  obj                if  ReferenceEquals null  obj   return false          if  ReferenceEquals this  obj   return true          return Equals obj Left  Left   amp  amp  Equals obj Right  Right              public override int GetHashCode                 unchecked                       return  Left GetHashCode     397    Right GetHashCode

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I ve also used tuples as jason in his answer does   However  I suggest you simply define a tuple as a struct   public struct Tuple lt T1  T2 gt        public readonly T1 Item1      public readonly T2 Item2      public Tuple T1 item1  T2 item2    Item1   item1  Item2   item2       public static class Tuple      for type-inference goodness      public static Tuple lt T1 T2 gt  Create lt T1 T2 gt  T1 item1  T2 item2             return new Tuple lt T1 T2 gt  item1  item2              You get immutability   GetHashcode and  Equals for free  which  while you re waiting for C  4 0  is nice  n simple     One warning however  the default GetHashcode implementation  sometimes  only considers the first field so make sure to make the first field the most discriminating or implement GetHashcode yourself  e g  using FieldwiseHasher Hash this  from ValueUtils   otherwise you ll likely run into scalability issues   Also  you get to avoid nulls which tend to complicate matters  and if you really want nulls  you just make your Tuple lt  gt  nullable    Slightly offtopic  am I the only one annoyed at the framework-level lack of support for non-null references   I work on large project  and occasionally a null creeps in somewhere it really shouldn t -- and hey presto  you get a nullreference exception -- but with a stack trace that points you to the reference s first usage  not the actually faulty code   Of course   NET 4 0 is pretty old by now  most of us can just use  NET 4 0 s tuple   Edit  to workaround the poor GetHashCode implementation that  NET provides for structs I ve written ValueUtils  which also allows you to use real names for your multi-field keys  that means you might write something like   sealed class MyValueObject   ValueObject lt MyValueObject gt        public DayOfWeek day      public string NamedPart        properties work fine too        which hopefully makes it easier to have human-readable names for data with value semantics  at least until some future version of C  implements proper tuples with named members  hopefully with decent hashcodes  -

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I wrote and have used this with success   public class MultiKeyDictionary lt K1  K2  V gt    Dictionary lt K1  Dictionary lt K2  V gt  gt          public V this K1 key1  K2 key2            get               if   ContainsKey key1      this key1  ContainsKey key2                   throw new ArgumentOutOfRangeException                return base key1  key2                     set               if   ContainsKey key1                   this key1    new Dictionary lt K2  V gt                 this key1  key2    value                       public void Add K1 key1  K2 key2  V value                if   ContainsKey key1                   this key1    new Dictionary lt K2  V gt                 this key1  key2    value             public bool ContainsKey K1 key1  K2 key2            return base ContainsKey key1   amp  amp  this key1  ContainsKey key2              public new IEnumerable lt V gt  Values           get               return from baseDict in base Values                    from baseKey in baseDict Keys                    select baseDict baseKey                         public class MultiKeyDictionary lt K1  K2  K3  V gt    Dictionary lt K1  MultiKeyDictionary lt K2  K3  V gt  gt        public V this K1 key1  K2 key2  K3 key3            get               return ContainsKey key1    this key1  key2  key3    default V                     set               if   ContainsKey key1                   this key1    new MultiKeyDictionary lt K2  K3  V gt                 this key1  key2  key3    value                       public bool ContainsKey K1 key1  K2 key2  K3 key3            return base ContainsKey key1   amp  amp  this key1  ContainsKey key2  key3            public class MultiKeyDictionary lt K1  K2  K3  K4  V gt    Dictionary lt K1  MultiKeyDictionary lt K2  K3  K4  V gt  gt        public V this K1 key1  K2 key2  K3 key3  K4 key4            get               return ContainsKey key1    this key1  key2  key3  key4    default V                     set               if   ContainsKey key1                   this key1    new MultiKeyDictionary lt K2  K3  K4  V gt                 this key1  key2  key3  key4    value                       public bool ContainsKey K1 key1  K2 key2  K3 key3  K4 key4            return base ContainsKey key1   amp  amp  this key1  ContainsKey key2  key3  key4            public class MultiKeyDictionary lt K1  K2  K3  K4  K5  V gt    Dictionary lt K1  MultiKeyDictionary lt K2  K3  K4  K5  V gt  gt        public V this K1 key1  K2 key2  K3 key3  K4 key4  K5 key5            get               return ContainsKey key1    this key1  key2  key3  key4  key5    default V                     set               if   ContainsKey key1                   this key1    new MultiKeyDictionary lt K2  K3  K4  K5  V gt                 this key1  key2  key3  key4  key5    value                       public bool ContainsKey K1 key1  K2 key2  K3 key3  K4 key4  K5 key5            return base ContainsKey key1   amp  amp  this key1  ContainsKey key2  key3  key4  key5            public class MultiKeyDictionary lt K1  K2  K3  K4  K5  K6  V gt    Dictionary lt K1  MultiKeyDictionary lt K2  K3  K4  K5  K6  V gt  gt        public V this K1 key1  K2 key2  K3 key3  K4 key4  K5 key5  K6 key6            get               return ContainsKey key1    this key1  key2  key3  key4  key5  key6    default V                     set               if   ContainsKey key1                   this key1    new MultiKeyDictionary lt K2  K3  K4  K5  K6  V gt                 this key1  key2  key3  key4  key5  key6    value                      public bool ContainsKey K1 key1  K2 key2  K3 key3  K4 key4  K5 key5  K6 key6            return base ContainsKey key1   amp  amp  this key1  ContainsKey key2  key3  key4  key5  key6            public class MultiKeyDictionary lt K1  K2  K3  K4  K5  K6  K7  V gt    Dictionary lt K1  MultiKeyDictionary lt K2  K3  K4  K5  K6  K7  V gt  gt        public V this K1 key1  K2 key2  K3 key3  K4 key4  K5 key5  K6 key6  K7 key7            get               return ContainsKey key1    this key1  key2  key3  key4  key5  key6  key7    default V                     set               if   ContainsKey key1                   this key1    new MultiKeyDictionary lt K2  K3  K4  K5  K6  K7  V gt                 this key1  key2  key3  key4  key5  key6  key7    value                      public bool ContainsKey K1 key1  K2 key2  K3 key3  K4 key4  K5 key5  K6 key6  K7 key7            return base ContainsKey key1   amp  amp  this key1  ContainsKey key2  key3  key4  key5  key6  key7            public class MultiKeyDictionary lt K1  K2  K3  K4  K5  K6  K7  K8  V gt    Dictionary lt K1  MultiKeyDictionary lt K2  K3  K4  K5  K6  K7  K8  V gt  gt        public V this K1 key1  K2 key2  K3 key3  K4 key4  K5 key5  K6 key6  K7 key7  K8 key8            get               return ContainsKey key1    this key1  key2  key3  key4  key5  key6  key7  key8    default V                     set               if   ContainsKey key1                   this key1    new MultiKeyDictionary lt K2  K3  K4  K5  K6  K7  K8  V gt                 this key1  key2  key3  key4  key5  key6  key7  key8    value                      public bool ContainsKey K1 key1  K2 key2  K3 key3  K4 key4  K5 key5  K6 key6  K7 key7  K8 key8            return base ContainsKey key1   amp  amp  this key1  ContainsKey key2  key3  key4  key5  key6  key7  key8            public class MultiKeyDictionary lt K1  K2  K3  K4  K5  K6  K7  K8  K9  V gt    Dictionary lt K1  MultiKeyDictionary lt K2  K3  K4  K5  K6  K7  K8  K9  V gt  gt        public V this K1 key1  K2 key2  K3 key3  K4 key4  K5 key5  K6 key6  K7 key7  K8 key8  K9 key9            get               return ContainsKey key1    this key1  key2  key3  key4  key5  key6  key7  key8  key9    default V                     set               if   ContainsKey key1                   this key1    new MultiKeyDictionary lt K2  K3  K4  K5  K6  K7  K8  K9  V gt                 this key1  key2  key3  key4  key5  key6  key7  key8  key9    value                      public bool ContainsKey K1 key1  K2 key2  K3 key3  K4 key4  K5 key5  K6 key6  K7 key7  K8 key8  K9 key9            return base ContainsKey key1   amp  amp  this key1  ContainsKey key2  key3  key4  key5  key6  key7  key8  key9            public class MultiKeyDictionary lt K1  K2  K3  K4  K5  K6  K7  K8  K9  K10  V gt    Dictionary lt K1  MultiKeyDictionary lt K2  K3  K4  K5  K6  K7  K8  K9  K10  V gt  gt        public V this K1 key1  K2 key2  K3 key3  K4 key4  K5 key5  K6 key6  K7 key7  K8 key8  K9 key9  K10 key10            get               return ContainsKey key1    this key1  key2  key3  key4  key5  key6  key7  key8  key9  key10    default V                     set               if   ContainsKey key1                   this key1    new MultiKeyDictionary lt K2  K3  K4  K5  K6  K7  K8  K9  K10  V gt                 this key1  key2  key3  key4  key5  key6  key7  key8  key9  key10    value                      public bool ContainsKey K1 key1  K2 key2  K3 key3  K4 key4  K5 key5  K6 key6  K7 key7  K8 key8  K9 key9  K10 key10            return base ContainsKey key1   amp  amp  this key1  ContainsKey key2  key3  key4  key5  key6  key7  key8  key9  key10            public class MultiKeyDictionary lt K1  K2  K3  K4  K5  K6  K7  K8  K9  K10  K11  V gt    Dictionary lt K1  MultiKeyDictionary lt K2  K3  K4  K5  K6  K7  K8  K9  K10  K11  V gt  gt        public V this K1 key1  K2 key2  K3 key3  K4 key4  K5 key5  K6 key6  K7 key7  K8 key8  K9 key9  K10 key10  K11 key11            get               return ContainsKey key1    this key1  key2  key3  key4  key5  key6  key7  key8  key9  key10  key11    default V                     set               if   ContainsKey key1                   this key1    new MultiKeyDictionary lt K2  K3  K4  K5  K6  K7  K8  K9  K10  K11  V gt                 this key1  key2  key3  key4  key5  key6  key7  key8  key9  key10  key11    value                      public bool ContainsKey K1 key1  K2 key2  K3 key3  K4 key4  K5 key5  K6 key6  K7 key7  K8 key8  K9 key9  K10 key10  K11 key11            return base ContainsKey key1   amp  amp  this key1  ContainsKey key2  key3  key4  key5  key6  key7  key8  key9  key10  key11

User · Answer

Many good solutions here  What I am missing here is an implementation based on the build in Tuple type  so I wrote one myself   Since it just inherits from Dictionary lt Tuple lt T1 T2 gt   T gt  you can always use both ways   var dict   new Dictionary lt int  int  Row gt     var row   new Row    dict Add 1  2  row   dict Add Tuple Create 1  2  row    dict Add new Tuple lt int  int gt  1  2      here is the code   public class Dictionary lt TKey1 TKey2 TValue gt     Dictionary lt Tuple lt TKey1  TKey2 gt   TValue gt   IDictionary lt Tuple lt TKey1  TKey2 gt   TValue gt         public TValue this TKey1 key1  TKey2 key2                get   return base Tuple Create key1  key2              set   base Tuple Create key1  key2     value               public void Add TKey1 key1  TKey2 key2  TValue value                base Add Tuple Create key1  key2   value              public bool ContainsKey TKey1 key1  TKey2 key2                return base ContainsKey Tuple Create key1  key2              Please be aware that this implementation depends on the Tuple Equals   implementation itself   http   msdn microsoft com en-us library dd270346 v vs 110  aspx  The obj parameter is considered to be equal to the current instance under the following conditions     It is a Tuple object   Its two components are of the same types as the current instance   Its two components are equal to those of the current instance  Equality is determined by the default object equality comparer for each component

User · Answer

Is there anything wrong with new Dictionary lt KeyValuePair lt object  object   object

User · Answer

Tuples will be  are  in  Net 4 0 Until then  you can also use a    Dictionary lt key1  Dictionary lt key2  TypeObject gt  gt     or  creating a custom collection class to represent this      public class TwoKeyDictionary lt K1  K2  T gt            Dictionary lt K1  Dictionary lt K2  T gt  gt        or  with three keys     public class ThreeKeyDictionary lt K1  K2  K3  T gt        Dictionary lt K1  Dictionary lt K2  Dictionary lt K3  T gt  gt  gt

[c#] Multi-key dictionary in c#?

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