How Can I Efficiently Merge Two Lists, Removing Duplicates, and Maintaining Order?

Merging Lists for a Concatenated Result

In this scenario, you have two lists of strings (or any arbitrary type) and desire to combine them swiftly while maintaining the original order. Additionally, you wish to eliminate any duplicate entries within the merged list. Despite researching this topic, you have not identified a straightforward solution and prefer to avoid implementing complex interfaces.

One effective approach is employing the AddRange method:

List<string> a = new List<string>();
List<string> b = new List<string>();

a.AddRange(b);

This approach preserves the order of elements in both lists, transferring the contents of b into a. However, it does not remove duplicates.

An alternative option that addresses the duplication issue is the Union method:

var newList = a.Except(b).ToList();

This line combines the elements of a and b, excluding any duplicates. The result is stored in a new list named newList.

Lastly, if you need to maintain the original lists, you can utilize the Concat method:

var newList = a.Concat(b);

This operation produces an IEnumerable object. It iterates over both lists, sequentially yielding their elements in the order they appear. If you need a list as the output, you can convert the IEnumerable to a List using the ToList method.

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