Split list into two lists with single LINQ statement [duplicate]

Question

I would like to split a list into two lists with a single LINQ statement. I'm currently doing this:

var listA = allItems.Where(item => item.IsUseful);
var listB = allItems.Except(listA);

But I want a single LINQ statement in query syntax that iterates over the original list only once, and returns an anonymous type with the two lists as properties (eg results.ListA; results.ListB).

Answer 1

This will give you a Dictionary<bool, List<T>> with two lists, which you can easily get your lists with result[true] and result[false]:

var result = allItems.GroupBy(item => item.IsUseful)
                     .ToDictionary(x => x.Key,x => x.ToList());