Question

I’m currently experimenting a bit with LINQ. Let’s say I have two collections of identical length:

var first = new string[] { "1", "2", "3" };
var second = new string[] { "a", "b", "c" };

I would like to merge those two collections into one, but in an interleaved fashion. The resulting sequence should thus be:

"1", "a", "2", "b", "3", "c"

What I’ve come up with so far is a combination of Zip, an anonymous type and SelectMany:

var result = first.Zip( second, ( f, s ) => new { F = f, S = s } )
                  .SelectMany( fs => new string[] { fs.F, fs.S } );

Does anybody know of an alternate/simpler way to achieve such an interleaved merge with LINQ?

Answer 1

Warning: this will skip trailing elements if the enumerations have different lengths. If you’d rather substitute in nulls to pad out the shorter collection, use Andrew Shepherd’s answer below.

---

You could write your own Interleave extension method, like in this example.

internal static IEnumerable<T> InterleaveEnumerationsOfEqualLength<T>(
    this IEnumerable<T> first, 
    IEnumerable<T> second)
{
    using (IEnumerator<T>
        enumerator1 = first.GetEnumerator(),
        enumerator2 = second.GetEnumerator())
    {
        while (enumerator1.MoveNext() && enumerator2.MoveNext())
        {
            yield return enumerator1.Current;
            yield return enumerator2.Current;
        }
    }
}