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Part 81 - When to use a dictionary over list in c#

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Part 80 - Some useful methods of List collection class

Find() method of the List class loops thru each object in the list until a match is found. So, if you want to lookup a value using a key, dictionary is better for performance over list. So, use dictionary when you know the collection will be primarily used for lookups.

Example code used in the demo
public class Program
    public static void Main()
        Country country1 = new Country()
            Code = "AUS",
            Name = "AUSTRALIA",
            Capital = "Canberra"

        Country country2 = new Country()
            Code = "IND",
            Name = "INDIA ",
            Capital = "New Delhi"

        Country country3 = new Country()
            Code = "USA",
            Name = "UNITED STATES",
            Capital = "Washington D.C."

        Country country4 = new Country()
            Code = "GBR",
            Name = "UNITED KINGDOM",
            Capital = "London"

        Country country5 = new Country()
            Code = "CAN",
            Name = "CANADA",
            Capital = "Ottawa"

        //List<Country> listCountries = new List<Country>();

        Dictionary<stringCountry> dictionaryCountries = new Dictionary<string, Country>();
        dictionaryCountries.Add(country1.Code, country1);
        dictionaryCountries.Add(country2.Code, country2);
        dictionaryCountries.Add(country3.Code, country3);
        dictionaryCountries.Add(country4.Code, country4);
        dictionaryCountries.Add(country5.Code, country5);

        string strUserChoice = string.Empty;
            Console.WriteLine("Please enter country code");
            string strCountryCode = Console.ReadLine().ToUpper();

            // Find() method of the list class loops thru each object in the list until a match
            // is found. 
So, if you want to lookup a value using a key dictionary is better 
            // for performance over list. 
            // Country resultCountry = listCountries.
            //                                    Find(country => country.Code == strCountryCode);

            Country resultCountry = dictionaryCountries.ContainsKey(strCountryCode) ?                 dictionaryCountries[strCountryCode] : null;

            if (resultCountry == null)
                Console.WriteLine("The country code you enetered does not exist");
                Console.WriteLine("Name = " + resultCountry.Name + " Captial =" + resultCountry.Capital);

                Console.WriteLine("Do you want to continue - YES or NO?");
                strUserChoice = Console.ReadLine().ToUpper();
            while (strUserChoice != "NO" && strUserChoice != "YES");
        while (strUserChoice == "YES");

public class Country
    public string Name { get; set; }
    public string Code { get; set; }
    public string Capital { get; set; }

1 comment:

  1. I suggested to use dictionary when the metadata should be lookups' values,and we knew the type of the keys and values of these lookups' values, otherwise use Hashtable


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