How to create and populate a nested dictionary with three keys

Question

I have a unique double corresponding to a variation of three strings. I want to populate a dictionary or something such that I can call something like dict[key1][key2][key3] and get the value.

I've tried a whole bunch of things like

    Dictionary<string, Dictionary<string, double>> dict = new Dictionary<string, Dictionary<string, double>> {
        { "Foo", {"Bar", 1.2 } },
        { "Foo", {"Test", 3.4 } }
    };

Which gives me syntax errors and errors like "Error 4 A namespace cannot directly contain members such as fields or methods"

And

    Dictionary<double, Tuple<string, string>> dict = {
          {1.23, "Blah", "Foo"}
    };

Which gives me errors like "Error 1 Can only use array initializer expressions to assign to array types. Try using a new expression instead."

And

    object dict = new Dictionary<string, Dictionary<string, Dictionary<string, string>>>();

    dict["k1"] = new Dictionary<string, Dictionary<string, string>>();
    dict["k1"]["k2"] = new Dictionary<string, string>();
    dict["k1"]["k2"]["k3"] = 3.5;

Which gives me syntax errors and errors like "Error 2 Invalid token '"k1"' in class, struct, or interface member declaration"

How should I go about this? Thanks in advance.

![enter image description here][1]

Edit: Trying Jonesy's code:

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        string[] grades = { "Grade 1", "Grade 5", "Grade 8", "ASTM A325", "316 Stainless", "Monel", "Brighton Best 1960" };
        string[] sizes = { "#1", "2", "3", "4", "5", "6", "8", "10", "12", "1/4", "5/16", "3/8", "7/16", "1/2", "9/16", "5/8", "3/4", "7/8", "1", "1-1/8", "1-1/4", "1-3/8", "1-1/2" };

        var dict = new Dictionary<string, Dictionary<string, Dictionary<string, double>>>();
        dict["k1"] = new Dictionary<string, Dictionary<string, double>>();
        dict["k1"]["k2"] = new Dictionary<string, double>();
        dict["k1"]["k2"]["k3"] = 3.5;


        public Form1()
        {
            InitializeComponent();
        } 

Answer 1

your last attempt is close, you want:

var dict = new Dictionary<string, Dictionary<string, Dictionary<string, double>>>();
dict["k1"] = new Dictionary<string, Dictionary<string, double>>();
dict["k1"]["k2"] = new Dictionary<string, double>();
dict["k1"]["k2"]["k3"] = 3.5;

you want var instead of object

(or Dictionary<string, Dictionary<string, Dictionary<string, double>>> if you like scrolling)

and your very last string should be a double.

Answer 2

As I understood, you have data and want to perform lookup in it. Why can't you just use some database for that purpose?

But if you really want to hardcode all values, you can. Just don't initialize dictionary manually, make simplifications - parse data in runtime.

Something like this. (I suppose, that you are novice in c# programming, so I've created new Console Application and copy-pasted all the code for your convenience)

public class Program
{
    // harcode all data as string
    const string RawData =
        "k11,k12,k13=3.4;" +
        "k21,k22,k23=4.42;" +
        "k31,k32,k33=5.91;" +
        "k41,k42,k43=8.14;" +
        "k51,k52,k53=4.13;" +
        "k61,k62,k63=5.4";

    static void Main(string[] args)
    {
        // create dictionary from hardcoded string
        var data = ParseData();

        // use Tuple as key for data lookup
        var value = data[Tuple.Create("k11", "k12", "k13")];

        // check, that value equals expected one
        Debug.Assert(value == 3.4);
    }

    private static IDictionary<Tuple<string, string, string>, double> ParseData()
    {
        var parsedData =
            RawData
                .Split(';')
                .Select(ParseRow)
                .ToDictionary(x => x.Item1, x => x.Item2);

        return parsedData;
    }

    private static Tuple<Tuple<string, string, string>, double> ParseRow(string row)
    {
        var parts = row.Split('=');
        var coefficients = ParseCoefficients(parts[0]);
        var value = Double.Parse(parts[1], CultureInfo.InvariantCulture);

        return Tuple.Create(coefficients, value);
    }

    private static Tuple<string, string, string> ParseCoefficients(string row)
    {
        var coeffs = row.Split(',');
        var result = Tuple.Create(coeffs[0], coeffs[1], coeffs[2]);

        return result;
    }
}

As another simplification, you can use custom class as dictionary key instead of nested dictionaries. Write your own(pay attention, that it should override equality members Equals and GetHashCode), or use something from base class library. Tuple<string, string, string> is the perfect one.