Question

Suppose I have 2 enumerations that I know have the same number of elements and each element “corresponds” with the identically placed element in the other enumeration. Is there a way to process these 2 enumerations simultaneously so that I have access to the corresponding elements of each enumeration at the same time?

Using a theoretical LINQ syntax, what I have in mind is something like:

from x in seq1, y in seq2
select new {x.foo, y.bar}

Answer 1

Since Neil Williams deleted his answer, I’ll go ahead and post a link to an implementation by Jon Skeet.

To paraphrase the relevant portion:

public static IEnumerable<KeyValuePair<TFirst,TSecond>> Zip<TFirst,TSecond>
    (this IEnumerable<TFirst> source, IEnumerable<TSecond> secondSequence)
{
    using (IEnumerator<TSecond> secondIter = secondSequence.GetEnumerator())
    {
        foreach (TFirst first in source)
        {
            if (!secondIter.MoveNext())
            {
                throw new ArgumentException
                    ("First sequence longer than second");
            }
            yield return new KeyValuePair<TFirst, TSecond>(first, secondIter.Current);
        }
        if (secondIter.MoveNext())
        {
            throw new ArgumentException
                ("Second sequence longer than first");
        }
    }        
}

Note that the KeyValuePair<> is my addition, and that I’m normally not a fan of using it this way. Instead, I would define a generic Pair or Tuple type. However, they are not included in the current version of the framework and I didn’t want to clutter this sample with extra class definitions.