How to use C# Dictionaries
In a nutshell:
Dictionaries can be used to store a list of items, but instead of using a standard flat “List” you can identify the records with a key.
First of all, make sure you’ve included the correct namespace:
using System.Collections.Generic;
Secondly you need to declare a dictionary.
For this example we are going to declare a dictionary called dicEmployees and within the dictionary we are going to store the identity number of the employee as well as their name.
Dictionary<int, string> dicEmployees = new Dictionary<int, string>();
Populating the Dictionary
Populating the dictionary is as easy as one-two-three…
dicEmployees.Add(14, “Marcus Orelius”);
In this case we’ve added Marcus Orelius with employee number 14 to our dictionary.
Retrieving Dictionary Values
Retrieving values are just as easy…
string sEmployeeName = dicEmployees[14];
Additional Options:
dicEmployees.ContainsKey(14); // Returns true/false; if the dictionary contains the key 14
dicEmployees.ContainsValue(”Marcus Orelius”); // Returns true/false; if the dictionary contains the value “Marcus Orelius”
dicEmployees.Count; // Returns the total item count in the dictionary (int)
dicEmployees.Keys; // Returns the “KeyCollection” list of the keys currently in the dictionary
dicEmployees.Values; // Returns a “ValueCollection” list of the values currently in the dictionary
Playing It Safe…
I highly recommend building in a safeguard when checking the values of a dictionary:
if(dicEmployees.ContainsKey(14))
return dicEmployees[14];
Dictionary of Dictionaries:
I recently tried a dictionary of dictionaries and was quite happy with the result. Let’s build on the previous example. Assume you want to store a list of years and include if Marcus ever took leave in those years. We are going to declare a dictionary of a dictionary which will enable us to store a list of employees and the years they worked plus if they ever went on leave…
Dictionary<int, Dictionary<int, bool>> dicEmployees = new Dictionary<int, Dictionary<int, bool>>();
Dictionary<int, bool> dicMarcus = new Dictionary<int, bool>();
//Add years and if Marcus ever took leave on those days
dicMarcus.Add(41, true);
dicMarcus.Add(42, true);
dicMarcus.Add(43, false);
dicMarcus.Add(44, true);
dicMarcus.Add(45, false);dicEmployees.Add(14, dicMarcus);
//Did Marcus take leave when he was 43?
bool wasMarcusAtWorkAged43 = dicEmployees[14][43];
// Value returned is false
Hope that helps…
