linq - Add two Lists of different length in c#

Question

List<double> a = new List<double>{1,2,3};
List<double> b = new List<double>{1,2,3,4,5};

a + b should give me 2,4,6,4,5

obvisouly i can write a loop but is there a better way? using linq?

Answer 1

You could use a modified "zip" operation easily enough, but nothing built in. Something like:

    static void Main() {
        var a = new List<int> { 1, 2, 3 };
        var b = new List<int> { 1, 2, 3, 4, 5 };
        foreach (var c in a.Merge(b, (x, y) => x + y)) {
            Console.WriteLine(c);
        }
    }
    static IEnumerable<T> Merge<T>(this IEnumerable<T> first,
            IEnumerable<T> second, Func<T, T, T> operation) {
        using (var iter1 = first.GetEnumerator())
        using (var iter2 = second.GetEnumerator()) {
            while (iter1.MoveNext()) {
                if (iter2.MoveNext()) {
                    yield return operation(iter1.Current, iter2.Current);
                } else {
                    yield return iter1.Current;
                }
            }
            while (iter2.MoveNext()) {
                yield return iter2.Current;
            }
        }
    }