How do I merge (or zip) two IEnumerables together?

Question

I have an IEnumerable<T> and an IEnumerable<U> that I want merged into an IEnumerable<KeyValuePair<T,U>> where the indexes of the elements joined together in the KeyValuePair are the same. Note I'm not using IList, so I don't have a count or an index for the items I'm merging. How best can I accomplish this? I would prefer a LINQ answer, but anything that gets the job done in an elegant fashion would work as well.

Answer 1

Note: As of .NET 4.0, the framework includes a .Zip extension method on IEnumerable, documented here. The following is maintained for posterity and for use in .NET framework version earlier than 4.0.

I use these extension methods:

// From http://community.bartdesmet.net/blogs/bart/archive/2008/11/03/c-4-0-feature-focus-part-3-intermezzo-linq-s-new-zip-operator.aspx
public static IEnumerable<TResult> Zip<TFirst, TSecond, TResult>(this IEnumerable<TFirst> first, IEnumerable<TSecond> second, Func<TFirst, TSecond, TResult> func) {
    if (first == null) 
        throw new ArgumentNullException("first");
    if (second == null) 
        throw new ArgumentNullException("second");
    if (func == null)
        throw new ArgumentNullException("func");
    using (var ie1 = first.GetEnumerator())
    using (var ie2 = second.GetEnumerator())
        while (ie1.MoveNext() && ie2.MoveNext())
            yield return func(ie1.Current, ie2.Current);
}

public static IEnumerable<KeyValuePair<T, R>> Zip<T, R>(this IEnumerable<T> first, IEnumerable<R> second) {
    return first.Zip(second, (f, s) => new KeyValuePair<T, R>(f, s));
}

EDIT: after the comments I'm obliged to clarify and fix some things:

• I originally took the first Zip implementation verbatim from Bart De Smet's blog
• Added enumerator disposing (which was also noted on Bart's original post)
• Added null parameter checking (also discussed in Bart's post)