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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 <string, string>

I now receive another similar dictionary, say:

NewAnimals <string,string>

How can I append the entire NewAnimals dictionary to Animals?

Accepted Answer

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<T>, and not just on Dictionary<TKey,TValue>.

public static void AddRange<T>(this ICollection<T> target, IEnumerable<T> 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)

Answer 2

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<T, S>(this Dictionary<T, S> source, Dictionary<T, S> 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<string,string> animals = new Dictionary<string,string>();
Dictionary<string,string> newanimals = new Dictionary<string,string>();

animals.AddRange(newanimals);

Answer 3

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<TKey, TValue>explicitly implements theICollection<KeyValuePair<TKey, TValue>>.Addmethod, you can also do this:

var animalsAsCollection = (ICollection<KeyValuePair<string, string>>) Animals;

foreach(var kvp in NewAnimals)
   animalsAsCollection.Add(kvp);

It's a pity the class doesn't have anAddRangemethod likeList<T> does.

Answer 4

The short answer is, you have to loop.

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Adding a Dictionary to Another [Duplicate]

5 Answers

Alexander Ross