How to modify key in a dictionary in C#

Question

How can I change the value of a number of keys in a dictionary.

I have the following dictionary :

SortedDictionary<int,SortedDictionary<string,List<string>>> 

I want to loop through this sorted dictionary and change the key to key+1 if the key value is greater than a certain amount.

Answer 1

As Jason said, you can't change the key of an existing dictionary entry. You'll have to remove/add using a new key like so:

// we need to cache the keys to update since we can't // modify the collection during enumeration var keysToUpdate = new List<int>();  foreach (var entry in dict) {     if (entry.Key < MinKeyValue)     {         keysToUpdate.Add(entry.Key);     } }  foreach (int keyToUpdate in keysToUpdate) {     SortedDictionary<string, List<string>> value = dict[keyToUpdate];      int newKey = keyToUpdate + 1;      // increment the key until arriving at one that doesn't already exist     while (dict.ContainsKey(newKey))     {         newKey++;     }      dict.Remove(keyToUpdate);     dict.Add(newKey, value); } 

Answer 2

You need to remove the items and re-add them with their new key. Per MSDN:

Keys must be immutable as long as they are used as keys in the SortedDictionary(TKey, TValue).