Dictionary with two keys and one value without hashing

Question

I'm looking for a better way to do the following.

using System;
using System.Collections;

Dictionary<int, string> namebyID = new Dictionary<int, string>();
Dictionary<string, int> idbyName = new Dictionary<string, int>();
Dictionary<string, string> valuebyName = new Dictionary<string, string>(); // users favorite dessert

/* Lets store information about "leethaxor" */
namebyID.Add(1234, "leethaxor");
idbyName.Add("leethaxor", 1234);
valuebyName.Add("leethaxor", "cake");

/* use case 1, I'm given an ID and i need the user's favorite dessert*/
if (namebyID.ContainsKey(1234))
{
    string username;
    namebyID.TryGetValue(1234, out username);
    if (valuebyName.ContainsKey(username))
    {
        string dessert;
        valuebyName.TryGetValue(username, out dessert);
        Console.Write("ID 1234 has a username of " + username + " and loves " + dessert + "\n");
    }
}

/* use case 2, I'm given a username and need to make sure they have a valid ID*/
if (idbyName.ContainsKey("leethaxor"))
{
    int id;
    idbyName.TryGetValue("leethaxor", out id);
    Console.Write("username leethaxor has a valid ID of " + id + "\n");
}

I'd really like to not use 3 different dictionaries, as the id, username, and value are all related to one another. Hashing key1(id) and key2(username) together won't work because I'm only given one or the other, not both.

Then you shoulr create a class that holds all these related information. — MakePeaceGreatAgain, Jan 21 '18 at 19:26
Please explain what is the "this" in "better way to do this". Makes it much easier to help — Gilad Green, Jan 21 '18 at 19:26
Is this the same question you posted earlier? https://stackoverflow.com/questions/48369716/c-sharp-dictionary-with-two-keys-and-value — DavidG, Jan 21 '18 at 19:29
@DavidG Seems to be the same context, but obviously OP already used the solution from what was suggested to him/her within that question. So That´s not a duplicate at all. — MakePeaceGreatAgain, Jan 21 '18 at 19:37

score 2 · Answer 1 · answered Jan 21 '18 at 19:43

You should definitly use your own class that holds all those information that belongs together. Relying on different dictionaries is a mess and gets really complex and complicated the more information you´r putting into those dictionaries.

So in your case you may create a class, let´s call it Person. Every Person has an Id, a UserName and a Value:

class Person
{
    public int Id { get; set; }
    public string UserName { get; set; }
    public string Value { get; set; }
}

Now create a list of those persons, e.g.:

var list = new List<Person> { 
    new Person { Id = 1234, UserName = "leethaxor", Value = "Cake" },
    new Person { Id = 2, UserName = "Berta", Value = "AnotherValue" }
};

Now you can get the person with a given Id or a given UserName:

var aPerson = list.FirstOrDefault(x => x.Id = 1234);

or

var aPerson = list.FirstOrDefault(x => x.UserName = "leethaxor");

You should definitly have a look on the basics of object-oriented programming, which is about objects and their behaviour.

Do note that looking up user by ID or Name using LINQ usually performs slower than using the key of a Dictionary. But it is unclear whether performance is a concern for the OP. — NightOwl888, Jan 21 '18 at 19:49
@NightOwl888 Fair point. However OP can still add the instances into a dictionary. Creating a class has nothing to do with this, only with how those instances are retrieved. — MakePeaceGreatAgain, Jan 22 '18 at 08:45

Bae · Answer 2 · 2018-01-21T19:53:14.533

1

Why not just use a class? Also, use TryGetValue() instead of ContainsKey(). What is more efficient: Dictionary TryGetValue or ContainsKey+Item?

public class User 
{
    public int Id;
    public string Name;
    public string Value;
}

Dictionary<int, User> userById = new Dictionary<int, User>();

edited Jan 21 '18 at 19:53

answered Jan 21 '18 at 19:31

Bae

88
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Dictionary with two keys and one value without hashing

2 Answers2