How Can I Use Lambda Expressions to Get Distinct Values in .NET?

Efficiently Identifying Unique Values in .NET with Lambda Expressions

Extracting unique elements from a collection is a frequent programming need. .NET's LINQ library offers the Distinct() method for this, but its limitations become apparent when dealing with custom objects requiring specific equality comparisons. While Distinct() accepts an IEqualityComparer, directly using lambda expressions for this comparison isn't natively supported.

A Concise Approach Using IEqualityComparer

One solution involves creating an IEqualityComparer inline:

<code class="language-csharp">var distinctValues = myCustomerList.Distinct(
    EqualityComparer<Customer>.Create((c1, c2) => c1.CustomerId == c2.CustomerId)
);</code>

This method, while functional, can feel somewhat cumbersome.

Alternative: Leveraging GroupBy and Select

A more elegant alternative bypasses the need for an explicit IEqualityComparer. This approach utilizes GroupBy and Select:

<code class="language-csharp">IEnumerable<Customer> filteredList = originalList
  .GroupBy(customer => customer.CustomerId)
  .Select(group => group.First());</code>

This groups elements based on the specified key (CustomerId in this case) and then selects the first item from each group, effectively filtering out duplicates. This provides a cleaner and more readable solution for achieving distinct values using lambda expressions.

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