Swap two items in List<T>

Question

Is there a LINQ way to swap the position of two items inside a List<T>?

Answer 1

Check the answer from Marc from C#: Good/best implementation of Swap method.

public static void Swap<T>(IList<T> list, int indexA, int indexB) {     T tmp = list[indexA];     list[indexA] = list[indexB];     list[indexB] = tmp; } 

which can be linq-i-fied like

public static IList<T> Swap<T>(this IList<T> list, int indexA, int indexB) {     T tmp = list[indexA];     list[indexA] = list[indexB];     list[indexB] = tmp;     return list; } 

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var lst = new List<int>() { 8, 3, 2, 4 }; lst = lst.Swap(1, 2); 

Answer 2

Maybe someone will think of a clever way to do this, but you shouldn't. Swapping two items in a list is inherently side-effect laden but LINQ operations should be side-effect free. Thus, just use a simple extension method:

static class IListExtensions {     public static void Swap<T>(         this IList<T> list,         int firstIndex,         int secondIndex     ) {         Contract.Requires(list != null);         Contract.Requires(firstIndex >= 0 && firstIndex < list.Count);         Contract.Requires(secondIndex >= 0 && secondIndex < list.Count);         if (firstIndex == secondIndex) {             return;         }         T temp = list[firstIndex];         list[firstIndex] = list[secondIndex];         list[secondIndex] = temp;     } }