How to use nested dictionary in C#?

Question

My requirement is

Dictionary<outerString, Dictionary<innerString, List<SelectListItem>>>

When I try to get the value of the inner Dictionary using key(outerString), it gives an error saying "cannot apply indexing with type of expression...............".

I have tried this

Dictionary<outerString, Dictionary<innerString, List<SelectListItem>>> dict1 = new
    Dictionary<outerString, Dictionary<innerString, List<SelectListItem>>>;

Dictionary<innerString, List<SelectListItem>> dict2 = dict1.values["outerString"];

Any quick help will be greatly appreciated.

Thx in advance.

Answer 1

I guess what you need is just:

Dictionary<innerString, List<SelectListItem>> dict = dict1["someKey"];

Answer 2

You just need to change the last line of your code snippet to (I assumed where you wrote inner string and outer string you must meant string):

var dict = dict1["someValue"];

Additionally, you could probably make your code much readable with the var keyword:

var dict1 = new Dictionary<string, Dictionary<string, List<SelectListItem>>>();
var dict = dict1["someValue"];

Answer 3

So outerString and innerString are types? Did you actually just want a nested dictionary string -> string -> List<SelectListItem> ? If not, you'll have to show us the definition of these types, and give the compiler some way to convert from the string you are trying to index with...

Answer 4

You were close:

Dictionary<outerString, Dictionary<innerString, List<SelectListItem>>> dict1 = new 
Dictionary<outerString, Dictionary<innerString, List<SelectListItem>>>(); 

// Get inner dictionary whose key is "someValue"
Dictionary<innerString, List<SelectListItem>> dict = dict1["someValue"]

Answer 5

Did I misunderstand you? This works fine

Dictionary<string, Dictionary<string, List<string>>> list = new Dictionary<string, Dictionary<string, List<string>>>();
list.Add("test", new Dictionary<string, List<string>>());
Dictionary<string, List<string>> inner = list["test"];

or

var list = new Dictionary<string, Dictionary<string, List<string>>>();
list.Add("test", new Dictionary<string, List<string>>());
Dictionary<string, List<string>> inner = list["test"];

Answer 6

In

Dictionary<string, Dictionary<string, List<T>> dict1 = 
    new Dictionary<string, Dictionary<string, List<T>>();

you need

List<T> list12 = dict1["key1"]["key2"];

---

List<int> list1 = new List<int>();
list1.Add(1);
list1.Add(2);

Dictionary<string, List<int>> innerDict = new Dictionary<string, List<int>>();
innerDict.Add("inner", list1);

Dictionary<string, Dictionary<string, List<int>>> dict1 =
    new Dictionary<string, Dictionary<string, List<int>>>();
dict1.Add("outer", innerDict);

List<int> list2 = dict1["outer"]["inner"];

Answer 7

How about you use an array of strings for a key, rather than trying to nest the dictionaries -

       Dictionary<string[], List<string>> dict = 
           new Dictionary<string[],List<string>>();

       string[] key = {"inner", "outer"};
       List<string> vals = new List<string>();

       dict.Add(key, vals);