Dictionary with list of strings as value

Question

I have a dictionary where my value is a List  When I add keys  if the key exists I want to add another string to the value  List   If the key doesn t exist then I create a new entry with a new list with a value  if the key exists then I jsut add a value to the List value ex   Dictionary lt string  List lt string gt  gt  myDic   new Dictionary lt string  List lt string gt  gt     myDic Add newKey  add to existing list lt strings gt  and not create new one

User · Answer

I d wrap the dictionary in another class   public class MyListDictionary        private Dictionary lt string  List lt string gt  gt  internalDictionary   new Dictionary lt string List lt string gt  gt          public void Add string key  string value                if  this internalDictionary ContainsKey key                         List lt string gt  list   this internalDictionary key               if  list Contains value     false                                list Add value                                   else                       List lt string gt  list   new List lt string gt                 list Add value               this internalDictionary Add key  list

User · Answer

Just create a new array in your dictionary  Dictionary lt string  List lt string gt  gt  myDic   new Dictionary lt string  List lt string gt  gt     myDic Add newKey  new List lt string gt  existingList

User · Answer

To do this manually  you d need something like   List lt string gt  existing  if   myDic TryGetValue key  out existing         existing   new List lt string gt         myDic key    existing       At this point we know that  existing  refers to the relevant list in the     dictionary  one way or another  existing Add extraValue     However  in many cases LINQ can make this trivial using ToLookup  For example  consider a List lt Person gt  which you want to transform into a dictionary of  surname  to  first names for that surname   You could use   var namesBySurname   people ToLookup person   gt  person Surname                                       person   gt  person FirstName

User · Answer

A simpler way of doing it is  var dictionary   list GroupBy it   gt  it Key  ToDictionary dict   gt  dict Key  dict   gt  dict Select item   gt  item value  ToList

[c#] Dictionary with list of strings as value

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