Eliminate consecutive duplicates of list elements

Question

Is there a \"nice\" way to eliminate consecutive duplicates of list elements?

Example:

[\"red\"; \"red\"; \"blue\"; \"green         


        

Answer 1

Here is my suggestion. It is similar to @AlexJ's answer, with the addition of an IEqualityComparer parameter that allows to customize the equality check. I also removed the otherwise correct separation of argument-check and implementation, because this solution is not intended to be of Library-grade quality. As for the name I adopted the ExcludeConsecutiveDuplicates from @AntonSemenov's answer.

public static IEnumerable ExcludeConsecutiveDuplicates(
    this IEnumerable source, IEqualityComparer comparer = null)
{
    if (source == null) throw new ArgumentNullException(nameof(source));
    comparer = comparer ?? EqualityComparer.Default;
    bool isFirst = true;
    TSource last = default;
    foreach (var item in source)
    {
        if (isFirst || !comparer.Equals(item, last)) yield return item;
        isFirst = false;
        last = item;
    }
}

Usage example:

var source = new string[]
{
    "Red", "red", "blue", "green", "green", "red", "red", "yellow",
    "WHITE", "white", "red", "white", "white"
};
var result = source.ExcludeConsecutiveDuplicates(StringComparer.OrdinalIgnoreCase);
Console.WriteLine($"Result: {String.Join(", ", result)}");

Output:

Result: Red, blue, green, red, yellow, WHITE, red, white

The advantage of this solution compared to the accepted answer is that it doesn't require a source of type IList to be efficient.