Parallel iteration in C#?

Question

Is there a way to do foreach style iteration over parallel enumerables in C#? For subscriptable lists, I know one could use a regular for loop iterati

Answer 1

Short answer, no. foreach works on only one enumerable at a time.

However, if you combine your parallel enumerables into a single one, you can foreach over the combined. I am not aware of any easy, built in method of doing this, but the following should work (though I have not tested it):

public IEnumerable Combine(params object[] sources)
{
    foreach(var o in sources)
    {
        // Choose your own exception
        if(!(o is IEnumerable)) throw new Exception();
    }

    var enums =
        sources.Select(s => ((IEnumerable)s).GetEnumerator())
        .ToArray();

    while(enums.All(e => e.MoveNext()))
    {
        yield return enums.Select(e => e.Current).ToArray();
    }
}

Then you can foreach over the returned enumerable:

foreach(var v in Combine(en1, en2, en3))
{
    // Remembering that v is an array of the type contained in en1,
    // en2 and en3.
}