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...

Thanks

Answer 1

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).

Answer 2

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
List<int> keysToUpdate = new List<int>();

foreach (KeyValuePair<int, SortedDictionary<string, List<string>>> 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);
}