Processing a C# Dictionary using LINQ

Question

How do I write the "// Display using Foreach" loop implementation using LINQ Lambda Expression / Statemene Expression?

I want to simplify my development and avoid nested foreach loops as much as possible. I am trying to include more logic with in the second foreach statement and I want to use Lambda / Statement expression.

 internal class Program
{
    internal class Country
    {
        public string CountryName { get; set; }
        public int CountryCode { get; set; }
    }
    static void Main(string[] args)
    {
        List<Country> countries = new List<Country>()
        {
            new Country{CountryName = "India", CountryCode=1},
            new Country{CountryName = "Andaman Nicobar", CountryCode=1},
            new Country{CountryName = "United States of America",  CountryCode=2},
            new Country{CountryName = "Alaska",  CountryCode=2},
            new Country{CountryName = "Hawaii",  CountryCode=2},
            new Country{CountryName = "United Kingdom", CountryCode=3},
            new Country{CountryName = "Australia", CountryCode=4}
        };

        Dictionary<int, List<Country>> countriesDictionary = new Dictionary<int, List<Country>>();
        foreach (Country country in countries)
        {
            if (!countriesDictionary.ContainsKey(country.CountryCode))
                countriesDictionary.Add(country.CountryCode, new List<Country>());
            countriesDictionary[country.CountryCode].Add(country);                
        }

       // Display using Foreach

        foreach (int key in countriesDictionary.Keys)
        {                             
            List<Country> dCountries = countriesDictionary[key];

            foreach (Country country in dCountries)
            {
                if (country.CountryCode.Equals(key))
                {
                    Console.WriteLine(country.CountryName);
                }                
            }
            Console.WriteLine();            
        }
        Console.ReadLine();
    }

Please suggest.

You already have filtered countries in `countriesDictionary` dictionary, why are you searching in `dCountries` in nested loop? — Sergey Berezovskiy, Jul 05 '13 at 13:50

Theraot · Answer 1 · 2018-05-22T23:38:49.837

This is another alternative:

countriesDictionary.ToList().ForEach
(
    pair =>
    {
        pair.Value.ForEach(country => Console.WriteLine(country.CountryName));
        Console.WriteLine();
    }
);

Also, this one based on ~~Romoku's Answer~~(the answer was removed):

var countriesDictionary = countries.ToLookup(x => x.CountryCode, x => x);

foreach(var countryGroup in countriesDictionary)
{
    foreach(var country in countryGroup)
    {
        Console.WriteLine(country.CountryName);
    }
    Console.WriteLine();
}

Sergey Berezovskiy · Accepted Answer · 2013-07-05T13:59:31.933

If you want to group countries by code, then you don't need two dictionaries. Use Enumerable.GroupBy

foreach(var codeGroup in countries.GroupBy(c => c.CountryCode))
{
    foreach(var country in codeGroup)
       Console.WriteLine(country.CountryName);

    Console.WriteLine();
}

Or just use your countriesDictionary (it already has countries grouped by code):

foreach(var kvp in countriesDictionary)
{
    foreach(var country in kvp.Value)
       Console.WriteLine(country.CountryName);

    Console.WriteLine();
}

score 3 · Answer 3 · answered Jul 05 '13 at 14:36

Though you probably have enough answers for the time being, this LINQ will compress your dictionary into a list of country names, allowing an easy foreach to display them.

    List<string> countryNames = countriesDictionary.SelectMany(
        pair=>pair.Value.Where(
            country=>country.CountryCode == pair.Key
        ).Select(x=>x.CountryName)).ToList();

    foreach (var name in countryNames)
        Console.WriteLine(name);

But the way your Dictionary is set up, the key should always match the country codes in the value, correct?

score 1 · Answer 4 · answered Jul 05 '13 at 14:02

1

Or just make it very easy... as already mentioned, you're already grouping by Country code...

        foreach (var country in countriesDictionary.SelectMany(pair => pair.Value))
        {
            Console.WriteLine(country.CountryName);
        }

answered Jul 05 '13 at 14:02

Jamie - Fenrir Digital Ltd

1,337
8
20

score 1 · Answer 5 · answered Jul 05 '13 at 14:22

One way could be like this,avoiding the first foreach with GroupBy,the just 1 foreach logic to print each country name with specified code:

Dictionary<int, List<Country>> countriesDictionary = countries.GroupBy(g => g.CountryCode).ToDictionary(k => k.Key, k => k.ToList());

foreach (int key in countriesDictionary.Keys)
{
      Console.WriteLine("****Countries with code {0}****",key);
      int count = 0;
      while (count < countriesDictionary[key].Count)
      {
            Console.WriteLine(countriesDictionary[key][count].CountryName);
            count++;
      }
      Console.WriteLine();
}

Console.ReadLine();

score 0 · Answer 6 · answered Jul 05 '13 at 14:03

I will use a extension to do it.

 static class CountryExtension
    {
        public static void WriteCountriesGroupyCountryCode(this IEnumerable<Country> list)
        {
            int currentCountry=int.MinValue;
            list.OrderBy(c => c.CountryCode).ThenBy(c=>c.CountryName).ToList().ForEach(c =>
            {
                if (currentCountry == int.MinValue)
                {
                    currentCountry = c.CountryCode;
                }
                else if (currentCountry != c.CountryCode)
                {
                    Console.WriteLine();
                    currentCountry = c.CountryCode;
                }
                Console.WriteLine(c.CountryName);
            });
        }
    }

Processing a C# Dictionary using LINQ

6 Answers6