Скачать или смотреть How to Compare Dictionary Keys with List Values in C# and Retrieve Matches, Including Duplicates

Learn how to effectively compare keys of a dictionary with values from a list in C# . This guide provides a step-by-step guide to returning all matching values, including duplicates.
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Comparing Dictionary Keys with List Values in C#

In programming, sometimes we need to compare data from different structures. A common scenario arises when we have a Dictionary and a List, and we want to match the keys of the dictionary with the values in the list. This is especially important in scenarios where we need to include not just unique matches but also duplicate values from the list. In this post, we will explore how to achieve this in C# using LINQ and iteration techniques.

The Problem

Let's say you have the following Dictionary and List:

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When you run a LINQ query to compare the dictionary against the list, like so:

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You may expect the output to include all matching values, including duplicates. However, you end up with:

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But what you really want is:

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How can we achieve this in C# ? Let's dive into the solution.

The Solution

To get the correct output that includes duplicates, there are two methods we will explore: using a LINQ query and using a foreach loop.

Method 1: Using a LINQ Query (Not Recommended for Duplicates)

Although we can write the query in a straightforward manner, it does not account for duplicates effectively:

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This line checks each item in the list against the dictionary keys and retrieves the corresponding values. However, since it uses Where and Select, every repeated item in the list will only lead to one matching dictionary value being retrieved.

Method 2: Using a foreach Loop (Recommended)

A more effective approach is to use a foreach loop. This method allows us to actively check each item in the list and insert every corresponding dictionary value into our results. Here’s how:

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Why This Works

Efficiency: By checking each item in the list against the dictionary with TryGetValue, we only look up the dictionary for each item once.

Includes Duplicates: This approach ensures that every time a key from the list matches a key in the dictionary, its value is added to the result list, regardless of how many times it appeared in the original list.

Example Output

When you run the foreach loop code with the given dictionary and list, you’ll achieve the following output:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

When comparing keys of a dictionary with values from a list in C# , especially when duplicates are expected, using a foreach loop with the TryGetValue method is a simplified and effective solution. This method efficiently captures all matches, allowing you to retrieve each corresponding value multiple times when necessary.

Implementing this solution will enhance your ability to manipulate data structures in C# effectively. Happy coding!