How to update the value stored in Dictionary in C

Question

How to update value for a specific key in a dictionary Dictionary lt string  int gt

User · Answer

You can follow this approach   void addOrUpdate Dictionary lt int  int gt  dic  int key  int newValue        int val      if  dic TryGetValue key  out val                    yay  value exists          dic key    val   newValue            else                  darn  lets add the value         dic Add key  newValue             The edge you get here is that you check and get the value of corresponding key in just 1 access to the dictionary   If you use ContainsKey to check the existance and update the value using dic key    val   newValue  then you are accessing the dictionary twice

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Just point to the dictionary at given key and assign a new value   myDictionary myKey    myNewValue

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update - modify existent only  To avoid side effect of indexer use   int val  if  dic TryGetValue key  out val            key exist     dic key    val     update or  add new if value doesn t exist in dic   dic key    val    for instance   d  Two     2     adds to dictionary because  two  not already present d  Two     22     updates dictionary because  two  is now present

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It s possible by accessing the key as index  for example   Dictionary lt string  int gt  dictionary   new Dictionary lt string  int gt     dictionary  test     1  dictionary  test      1  Console WriteLine  dictionary  test        will print 2

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This may work for you   Scenario 1  primitive types  string keyToMatchInDict    x   int newValToAdd   1  Dictionary lt string int gt  dictToUpdate   new Dictionary lt string int gt   x  1    if  dictToUpdate ContainsKey keyToMatchInDict      dictToUpdate Add keyToMatchInDict  newValToAdd    else    dictToUpdate keyToMatchInDict    newValToAdd    or you can do operations such as    dictToUpdate keyToMatchInDict     newValToAdd    Scenario 2  The approach I used for a List as Value  int keyToMatch   1  AnyObject objInValueListToAdd   new AnyObject  something for the Ctor   Dictionary lt int List lt AnyObject gt  dictToUpdate   new Dictionary lt int List lt AnyObject gt       imagine this dict got initialized before with valid Keys and Values     if  dictToUpdate ContainsKey keyToMatch      dictToUpdate Add keyToMatch new List lt AnyObject gt  objInValueListToAdd    else    dictToUpdate keyToMatch    objInValueListToAdd    Hope it s useful for someone in need of help

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Here is a way to update by an index much like foo x    9 where x is a key and 9 is the value  var views   new Dictionary lt string  bool gt      foreach  var g in grantMasks        string m   g ToString        for  int i   0  i  lt   m Length  i                  views views ElementAt i  Key    m i  Equals  1     true   false

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Use LINQ  Access to dictionary for the key and change the value  Dictionary lt string  int gt  dict   new Dictionary lt string  int gt     dict   dict ToDictionary kvp   gt  kvp Key  kvp   gt  kvp Value   1

[c#] How to update the value stored in Dictionary in C#?

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