Question

If I have variable of type IEnumerable<List<string>> is there a LINQ statement or lambda expression I can apply to it which will combine the lists returning an IEnumerable<string>?

Answer 1

SelectMany – i.e.

        IEnumerable<List<string>> someList = ...;         IEnumerable<string> all = someList.SelectMany(x => x); 

For each item in someList, this then uses the lambda ‘x => x’ to get an IEnumerable<T> for the inner items. In this case, each ‘x’ is a List<T>, which is already IEnumerable<T>.

These are then returned as a contiguous block. Essentially, SelectMany is something like (simplified):

static IEnumerable<TResult> SelectMany<TSource, TResult>(     this IEnumerable<TSource> source,     Func<TSource, IEnumerable<TResult>> selector) {      foreach(TSource item in source) {       foreach(TResult result in selector(item)) {         yield return result;       }     } } 

Although that is simplified somewhat.