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C# Copy DictionaryCopy all the elements in a Dictionary collection into another.
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Copy Dictionary. The Dictionary has a copy constructor. When you pass an existing Dictionary to its constructor, it is copied. This is an effective way to copy a Dictionary's data.

Notes, original. When the original Dictionary is modified, the copy is not affected. Once copied, a Dictionary has separate memory locations to the original.

Constructor

Dictionary

First example. We can use a custom loop over the keys, but this is prone to code duplication and errors. It makes no sense to write the loop yourself.

Part A We copy the Dictionary into the second Dictionary "copy" by using the copy constructor.

Part B The code adds a key to the first Dictionary. And we see that the key added after the copy was made is not in the copy.

Part C We print the contents of both collections. The example demonstrates how the internal structures are copied.

Console

C# program that copies entire Dictionary
using System; using System.Collections.Generic; class Program { static void Main() { Dictionary<string, int> dictionary = new Dictionary<string, int>(); dictionary.Add("cat", 1); dictionary.Add("dog", 3); dictionary.Add("iguana", 5); // Part A: copy the Dictionary to a second object. Dictionary<string, int> copy = new Dictionary<string, int>(dictionary); // Part B: change the first Dictionary. dictionary.Add("fish", 4); // Part C: display the 2 Dictionaries. Console.WriteLine("--- Dictionary 1 ---"); foreach (var pair in dictionary) { Console.WriteLine(pair); } Console.WriteLine("--- Dictionary 2 ---"); foreach (var pair in copy) { Console.WriteLine(pair); } } }
--- Dictionary 1 --- [cat, 1] [dog, 3] [iguana, 5] [fish, 4] --- Dictionary 2 --- [cat, 1] [dog, 3] [iguana, 5]

Internals. The Dictionary constructor that accepts IDictionary is implemented with this loop. My research established that the foreach-loop is fast and eliminates lookups.

Foreach

IDictionary

Also We could easily adapt the loop to copy to a Hashtable or List of KeyValuePair structs.

KeyValuePair

Implementation of Dictionary copy constructor: C#
foreach (KeyValuePair<TKey, TValue> pair in dictionary) { this.Add(pair.Key, pair.Value); }

A summary. In C# we copied an entire Dictionary to a new Dictionary. As Dictionary does not define a Copy or CopyTo method, the copy constructor is the easiest way.

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