C#: How to iterate over a dictionary?

Apr 20, 2024  • C#

It’s common to use Dictionaries when working with data in C#. Dictionaries are an easy way to work with a collection of key/value pairs. A common task performed is to iterate over a dictionary. This enables you to access and manipulate the key/value pairs within the dictionary. In this article, we will take a look at methods of iterating over a dictionary in C#, as well as iterating over the collection of keys and values contained within the dictionary.

Defining a Dictionary in C#

Before we get into method of iteration, let’s take a look at the essentials needed to understand how to define and populate a dictionary in C#.

In C#, dictionaries are implemented using the generic System.Collections.Generic.Dictionary<TKey, TValue> class, where TKey represents the type of keys and TValue represents the type of values stored within the dictionary.

Here’s how you can define a dictionary:

Dictionary<string, int> myDictionary = new Dictionary<string, int>();

In this example, we’re creating a dictionary where keys are of type string and values are of type int. You can replace these types with any other valid C# data types based on your requirements.

Once you’ve defined your dictionary, you can populate it with key/value pairs using the .Add() method or by initializing it with initial values using collection initializers.

Here are examples of both of these methods:

// Adding key/value pairs individually
myDictionary.Add("apple", 10);
myDictionary.Add("banana", 20);
myDictionary.Add("orange", 15);

// Initializing dictionary with initial values using collection initializer
Dictionary<string, int> anotherDictionary = new Dictionary<string, int>()
{
    { "apple", 10 },
    { "banana", 20 },
    { "orange", 15 }
};

Once the dictionary is defined and populated with data, you can proceed to iterate over its elements as needed.

Iterating over C# Dictionary Key/Value Pairs

Suppose you have a dictionary named myDictionary and you want to iterate over the key/value pairs within the dictionary. You can use a foreach or any other loop within C#.

Here’s an example of doing this:

foreach(var item in myDictionary)
{
  foo(item.Key);
  bar(item.Value);
}

In this example, item represents a key/value pair where item.Key accesses the key and item.Value accesses the corresponding value. You can perform any desired operations within the loop using these components as needed.

Iterating over C# Dictionary Keys Only

There are instances where you may only need to iterate over the keys of the key/value pairs within the dictionary. In this case, you can directly iterate over the .Keys collection:

foreach(var item in myDictionary.Keys)
{
  foo(item);
}

In this example, item represents each key in the dictionary, allowing you to perform operations specific to keys without accessing their corresponding values.

Iterating over C# Dictionary Values Only

Similarly, if you only need to access the values stored within the dictionary, you can iterate over the .Values collection:

foreach(var item in myDictionary.Values)
{
  foo(item);
}

In this example, item represents each value in the dictionary (without the key), enabling you to manipulate values independently of their associated keys.

Conclusion

Understanding how to iterate over a dictionary in C# is fundamental for effectively working with key/value pair data. Whether you need to access key/value pairs together, iterate over keys exclusively, or process values alone, the flexibility of C# provides concise solutions for each of these scenarios.

Happy coding!

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