How Can I Use Lambda Expressions for Custom Distinct() Operations on Enumerable Objects?

Use Lambda expressions to customize the Distinct() operation

When dealing with enumerable objects, the Distinct() method provides a direct way to remove duplicate values. However, for objects that require custom equality checks, the existing Distinct() overloaded methods are not ideal.

One might expect an overloaded method that accepts a Lambda expression to define equality, for example:

<code class="language-c#">var distinctValues = myCustomerList.Distinct((c1, c2) => c1.CustomerId == c2.CustomerId);</code>

However, such overloaded methods do not exist in native methods. Instead, IEqualityComparer<T> instances must be used, which can be lengthy and cumbersome.

Alternatives

To achieve the desired functionality, you can combine the GroupBy() and Select() methods:

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

This method identifies and groups items based on the CustomerId field. The First() method then selects the first item from each group, effectively removing duplicates.

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