Today I was doing some LINQ to objects. I was replacing a pair of nested foreach loops which built a string list and was looking for an elegant way to do it in LINQ. I ran into the problem that I needed to convert a list of lists to a single list. The following extension method works great for that. Works great for merging arrays of arrays without copying anything.

          
            public
            static
            class ExtensionMethods
{ publicstatic IEnumerable<T>
UnionAll<T>(this IEnumerable<IEnumerable<T>>
eet) { foreach (var
et in eet) foreach (var
t in et)
yield return t;
} }