Iterate Over Dictionary in C# (Various ways)

In this article, I have mentioned how we can iterate over a dictionary in C# using foreach or using for loop or using ParallelEnumerable.ForAll() with console application example.

Using Foreach

Simplest way to loop dictionary is to use Foreach loop

using System;
using System.Collections.Generic;

namespace IterateDictionary
{
    public class Program
    {
        static void  Main(string[] args)
        {
            Dictionary<int, string> countryNames = new Dictionary<int,string>();
            countryNames.Add(1, "India");
            countryNames.Add(2, "Australia");
            countryNames.Add(3, "United States");
            countryNames.Add(4, "United Kingdom");

           foreach(var item in countryNames)
           {
                Console.WriteLine("Key: " + item.Key + "    Value:" + item.Value);
           }
        }

    }
}

Output:

Key: 1    Value:India
Key: 2    Value:Australia
Key: 3    Value:United States
Key: 4    Value:United Kingdom

The item variable in the above code of foreach loop will have KeyValuePair<TKey, TValue> type.

Using For Loop

You can also use for loop instead of foreach loop in some situations when you need a specific position element, but we will have to use Linq in this method to retrieve dictionary item at a particular positions.

using System;
using System.Collections.Generic;
using System.Linq;

namespace IterateDictionary
{
    public class Program
    {
        static void  Main(string[] args)
        {
            Dictionary<int, string> countryNames = new Dictionary<int,string>();
            countryNames.Add(1, "India");
            countryNames.Add(2, "Australia");
            countryNames.Add(3, "United States");
            countryNames.Add(4, "United Kingdom");

            for (int i = 0; i < countryNames.Count; i++)
            {
                var item = countryNames.ElementAt(i);
                Console.WriteLine(item.Value);
            }
        }

    }
}

Output:

India
Australia
United States
United Kingdom

Using ParallelEnumerable.ForAll()

ParallelEnumerable.ForAll() can be used if you have a large dictionary, we can make use of Parallel Language Integrated Query (LINQ) query.

using System;
using System.Collections.Generic;
using System.Linq;

namespace IterateDictionary
{
    public class Program
    {
        static void  Main(string[] args)
        {
            Dictionary<int, string> countryNames = new Dictionary<int,string>();
            countryNames.Add(1, "India");
            countryNames.Add(2, "Australia");
            countryNames.Add(3, "United States");
            countryNames.Add(4, "United Kingdom");

            countryNames.AsParallel().ForAll(country => Console.WriteLine("Key: " + country.Key + "    Value:" + country.Value));
        }

    }
}

Output:

Key: 3    Value:United States
Key: 1    Value:India
Key: 4    Value:United Kingdom
Key: 2    Value:Australia

If you will check above output, you will see it when using AsParallel.ForAll, key/value is printed randomly rather than in sequence.

Best way to loop the dictionary in C#

Even though we have multiple ways to iterate over dictionary key values, prefer using a simple foreach loop.

If you want to loop only C# dictionary Keys or Values use dictionary.Keys or dictionary.Values instead of an iterating the entire dictionary.

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