Adding a dictionary to another

Question

Possible Duplicates    Merging dictionaries in C    What s the fastest way to copy the values and keys from one dictionary into another in C       I have a dictionary that has some values in it  say   Animals  lt string  string gt    I now receive another similar dictionary  say   NewAnimals  lt string string gt    How can I append the entire NewAnimals dictionary to Animals

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The short answer is  you have to loop   More info on this topic   What  39 s the fastest way to copy the values and keys from one dictionary into another in C

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foreach var newAnimal in NewAnimals      Animals Add newAnimal Key newAnimal Value    Note  this throws an exception on a duplicate key     Or if you really want to go the extension method route I wouldn t   then you could define a general AddRange extension method that works on any ICollection lt T gt   and not just on Dictionary lt TKey TValue gt    public static void AddRange lt T gt  this ICollection lt T gt  target  IEnumerable lt T gt  source        if target  null        throw new ArgumentNullException nameof target        if source  null        throw new ArgumentNullException nameof source        foreach var element in source          target Add element        throws on duplicate keys for dictionaries

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You can loop through all the Animals using foreach and put it into NewAnimals

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Create an Extension Method most likely you will want to use this more than once and this prevents duplicate code   Implementation    public static void AddRange lt T  S gt  this Dictionary lt T  S gt  source  Dictionary lt T  S gt  collection             if  collection    null                        throw new ArgumentNullException  Collection is null                       foreach  var item in collection                        if  source ContainsKey item Key                    source Add item Key  item Value                             else                                 handle duplicate key issue here                                 Usage   Dictionary lt string string gt  animals   new Dictionary lt string string gt     Dictionary lt string string gt  newanimals   new Dictionary lt string string gt      animals AddRange newanimals

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The most obvious way is   foreach var kvp in NewAnimals     Animals Add kvp Key  kvp Value        use Animals kvp Key    kvp Value instead if duplicate keys are an issue   Since Dictionary lt TKey  TValue gt explicitly implements theICollection lt KeyValuePair lt TKey  TValue gt  gt  Addmethod  you can also do this   var animalsAsCollection    ICollection lt KeyValuePair lt string  string gt  gt   Animals   foreach var kvp in NewAnimals     animalsAsCollection Add kvp     It s a pity the class doesn t have anAddRangemethod likeList lt T gt  does

[c#] Adding a dictionary to another

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