How Can I Efficiently Concatenate Two Lists in C# While Removing Duplicates?

Combining Disparate Lists: A Swift Concatenation Technique

When faced with the task of merging two lists of arbitrary type, a straightforward and efficient approach is crucial. Let's delve into a method tailored to this specific scenario.

The goal is to concatenate the lists while preserving their order and eliminating duplicate elements. Fortunately, the .NET framework provides an elegant solution.

List<string> firstList = new List<string>();
List<string> secondList = new List<string>();

firstList.AddRange(secondList);

The AddRange method effortlessly appends the contents of secondList onto the end of firstList. This action seamlessly merges the two lists, maintaining their original order. However, it's worth noting that any duplicate elements present in secondList will be added to firstList without hesitation.

If your goal is to preserve both lists in their original form while creating a combined representation, consider utilizing the Concat method instead:

var combinedList = firstList.Concat(secondList);

Concat returns an IEnumerable object, which provides a lazy evaluation mechanism. No actual concatenation occurs until the IEnumerable object is iterated upon. This approach ensures that neither firstList nor secondList is modified in the process.

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