How to add value for Complex Dictionary?

Question

Hi,

As i know, the method to add values for dictionary as below.

    Dictionary<string, string> myDict = new Dictionary<string, string>();

    myDict.Add("a", "1");

If I declared "myDictDict" as the style below.

IDictionary<string, Dictionary<string, string>> myDictDict = new Dictionary<string, Dictionary<string, string>>();

myDictDict .Add("hello", "tom","cat"); ?// How to add value here.

thank you.

Answer 1

IDictionary<string,Dictionary<string,string>> myDictDict = new Dictionary<string,Dictionary<string,string>>();
Dictionary<string,string> dict = new Dictionary<string, string>();
dict.Add ("tom", "cat");
myDictDict.Add ("hello", dict);

Answer 2

IDictionary<string, Dictionary<string, string>> myDictDict = new Dictionary<string, Dictionary<string, string>>();

var subDict = new Dictionary<string, string>();
myDictDict .Add("hello", subDict ); 
subDict.Add("tom", "cat");

Answer 3

The proper way is like this:

// myDictDict is Dictionary<string, Dictionary<string, string>>
Dictionary<string, string> myDict;
string key = "hello";
if (!myDictDict.TryGetValue(key, out myDict)) {
    myDict = new Dictionary<string, string>();
    myDictDict.Add(key, myDict);
}
myDict.Add("tom", "cat");

This will extract the dictionary corresponding to the key (hello in your example) or create it if necessary and then will add the key/value pair to that dictionary. You could even extract this into an extension method.

static class Extensions {
    public static void AddToNestedDictionary<TKey, TNestedDictionary, TNestedKey, TNestedValue>(
        this IDictionary<TKey, TNestedDictionary> dictionary,
        TKey key,
        TNestedKey nestedKey,
        TNestedValue nestedValue
    ) where TNestedDictionary : IDictionary<TNestedKey, TNestedValue> {
        dictionary.AddToNestedDictionary(
            key,
            nestedKey,
            nestedValue,
            () => (TNestedDictionary)(IDictionary<TNestedKey, TNestedValue>)
                new Dictionary<TNestedKey, TNestedValue>());
    }

    public static void AddToNestedDictionary<TKey, TNestedDictionary, TNestedKey, TNestedValue>(
        this IDictionary<TKey, TNestedDictionary> dictionary,
        TKey key,
        TNestedKey nestedKey,
        TNestedValue nestedValue,
        Func<TNestedDictionary> provider
    ) where TNestedDictionary : IDictionary<TNestedKey, TNestedValue> {
        TNestedDictionary nested;
        if (!dictionary.TryGetValue(key, out nested)) {
            nested = provider();
            dictionary.Add(key, nested);
        }
        nested.Add(nestedKey, nestedValue);
    }
}

I left out guarding against null input to keep the idea clear. Usage:

myDictDict.AddToNestedDictionary(
    "hello",
    "tom",
    "cat",
    () => new Dictionary<string, string>()
);

or

myDictDict.AddToNesteDictionary("hello", "tom", "cat");

Answer 4

You can use C# 3's collection initializers, like this:

IDictionary<string, Dictionary<string, string>> myDictDict = new Dictionary<string, Dictionary<string, string>> {
    { "hello", new Dictionary<string, string> { "Tom", "Cat" } }
};

If the dictionary already exists, you can write

dict.Add("hello", new Dictionary<string, string> { "Tom", "Cat" });

Note that this will only work if hello isn't an existing key in the outer dictionary. If it might be, you should use Jason's answer.

Answer 5

You can define an extension method like this :

static void Add(this IDictionary<string, Dictionary<string, string>> dict, string a, string b, string c){
    dict.Add(a, new Dictionary<string,string>(){{b,c}};
}

and then use it as :

myDictDict.Add("hello", "tom","cat");

Answer 6

To handle this the "simple" way : something like this :

    myDictDict.Add("some string", new Dictionary<string, string>());

    myDictDict["some string"].Add("another", "string");

To respond directly to the OP's test case : (note the edit added below reflects a desire to correct the syntax of SLaks's answer : code tested and validated against Framework 3.5 Client profile in VS 2010 Beta 2)

    // a simple case of creating an instance of a dictionary
    // of type <string, string>
    // and using .NET 3.0's (FrameWork => 3.5) collection initializer syntax
    Dictionary<string, string> twoStringDict = new Dictionary<string, string>()
    {
      {"key one", "value one"},
      {"key two", "value two"}, // note : an "extra" comma does not cause an error here
    };

    // more complex case as in the question on StackOverFlow
    // where dictionary is type <string, Dictionary<string, string>>
    // and using .NET 3.0's (FrameWork => 3.5) collection initializer syntax
    Dictionary<string, Dictionary<string, string>> myDictDict = new Dictionary<string, Dictionary<string, string>>()
    {
      { "key one",
            new Dictionary<string, string>() { { "innerKeyOne", "innerValueOne" }}},
      { "key two",
            new Dictionary<string, string>() { { "innerKeyTwo", "innerValueTwo" }}}
    };

    // syntax for adding another key value pair to the complex case
    myDictDict.Add("key three", new Dictionary<string, string>() { { "innerKeyThree", "innerValueThree" }});