Indexed retrieval SortedDictionary<>

Question

I read here that SortedDictionary does not allow indexed retrieval unlike SortedList. Then how can I get the nameAddr["C"] correctly in the following code snippet?

        SortedDictionary<string, string> nameAddr = new SortedDictionary<string, string>();
        nameAddr.Add("X", "29");
        nameAddr.Add("A", "30");
        nameAddr.Add("C", "44");           

        Console.WriteLine(nameAddr["C"]);

Answer 1

That's indexing by key. SortedList allows indexing by "index of key", e.g. nameAddr.Values[1] would return "44".

(The collection doesn't allow indexing of name/value pair, just of each of Keys and Values separately.)

For example:

var list = new SortedList<string, string>
{
    { "X", "29" },
    { "A", "30" },
    { "C", "44" },
};

Console.WriteLine(list.Keys[1]); // Prints "C"
Console.WriteLine(list.Values[1]); // Prints "44"

Answer 2

SortedList internally uses an array as the data structure for storage and then just sorts the array as needed to keep the items in order. Since it uses an array the items can be accessed using a numeric index like you would for any array.

SortedDictionary internally uses a red-black binary search tree to keep the items in order. The concept is completely different. There is no array and no analog for retrieving the items by a numeric index. Your only option is to use the key portion of the key-value pair that was added to the dictionary.

With that said. Your code looks correct to me. That is the only way to retrieve items from the dictionary (other than using than Values collection, but that will not give you the numeric indexing ability either).