Maintain subsequence order in OrderBy

Question

Suppose I have a class with an integer Day property and an IEnumerable of objects where the days are 2, 3, 4, 1, 3, 3 and 5 (in that order

Answer 1

OrderBy is documented as being stable, if that is what you mean; so: you shouldn't need to do anything.

Enumerable.OrderBy

This method performs a stable sort; that is, if the keys of two elements are equal, the order of the elements is preserved. In contrast, an unstable sort does not preserve the order of elements that have the same key.