how do i clone a dictionary in C#

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4.83/5 (6 votes)

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C#

C#4.0

How do I clone a dictionary?
If I change a source dictionary, the new dictionary should not get changed.
Any idea?

Posted 7-Mar-11 20:31pm

vivektp

Updated 7-Mar-11 21:13pm

Sergey Alexandrovich Kryukov

v2

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Sergey Alexandrovich Kryukov 8-Mar-11 3:13am

I like Question, my 5.
(However, there are problems. You need to use correct capitalization, punctuation and spelling. For such a case, I'll do a fix, but please remember about it next time -- this is a matter of politeness.)
--SA

4 solutions

Solution 3

Using LINQ it would be something like:

var originalDictionary = ...;
var clonedDictionary = originalDictionary.ToDictionary(
    x => x.Key, // Typically no cloning necessary (immuable)
    x => (TargetType)x.Value.Clone()  // Do the copy how you want
);

This could be the prefered method to uses if your existing dictionary values each have their way to be copied...

Posted 18-Jul-11 16:26pm

Philippe Mori

v2

Solution 5

If the Type of the Value component of your Dictionary is not a reference Type, then you can use the Dictionary constructor that takes an existing Dictionary as an argument to clone it.

C#

public Dictionary<int, string> sourced = new Dictionary<int, string>
{
    {0,"string0"},{1, "string1"}
};

// test in some method
Dictionary<int,> newd = new Dictionary<int,>(sourced);
newd[1] = "hello";

// now examine value in 'sourced: note there is no change

Posted 6-Dec-15 7:10am

BillWoodruff

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Maciej Los 6-Dec-15 15:17pm

Bill, this is very old question. I've seen many valueable answers which have been down-voted because of it.

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OriginalGriff · Accepted Answer · 2011-03-07T20:46:00

You need to implement ICloneable.
Define your dictionary as a class, derived from Dictionary:

C#

public class CloneableDictionary<TKey, TValue> : Dictionary<TKey, TValue> where TValue : ICloneable
    {
    public CloneableDictionary<TKey, TValue> Clone()
        {
        CloneableDictionary<TKey, TValue> clone = new CloneableDictionary<TKey, TValue>();
        foreach (KeyValuePair<TKey, TValue> kvp in this)
            {
            clone.Add(kvp.Key, (TValue) kvp.Value.Clone());
            }
        return clone;
        }
    }

Then you can use the Clone method:

C#

CloneableDictionary<int, string> dic = new CloneableDictionary<int, string>() {
    {1, "Key1"},
    {2, "Key2"}};
CloneableDictionary<int, string> dicCopy = dic.Clone();
dicCopy[1] = "Key Changed";
foreach (KeyValuePair<int, string> kvp in dic)
    {
    Console.WriteLine(kvp.Key.ToString() + ":" + kvp.Value);
    }
foreach (KeyValuePair<int, string> kvp in dicCopy)
    {
    Console.WriteLine(kvp.Key.ToString() + ":" + kvp.Value);
    }

Sergey Alexandrovich Kryukov · Accepted Answer · 2011-03-07T20:49:00

I understand: your second line explains the meaning of the world "clone".

This is a problem of deep cloning. The deep cloning is always a custom stuff, to some extend.

You can simply create a new dictionary, take a loop by all key-value pairs and than add each element to your new dictionary. It will perfectly work if your key and value types are all of the value type or string type. In all other cases you need to insert in new dictionary not the keys and values from your old dictionary, but their clones. The problem is how deep is the cloning of the key and value?

If you need to do it once just for the pair of types, this is not a problem. How to make it generic?
…when I was preparing my code I found that Griff already answered correctly. Please use his answer.

My only extra note is this: the customization of this code is reduced to implementation of IClonable in your value type. You need to provide required level of cloning, because if your have, say, a value type containing reference type containing another reference type, and you need to change the most deep type's value, your shallow cloning maybe not deep enough.

Strictly speaking, you may need to clone keys as well (and apply IClonable in generic constraint) but in practice this should redundant because the functionality of the keys in the dictionary imply they should be immutable.

—SA