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copied!<p><strong>Update:</strong></p> <p>Eric Lippert recently posted on this: <a href="http://blogs.msdn.com/ericlippert/archive/2009/05/07/zip-me-up.aspx" rel="nofollow noreferrer">http://blogs.msdn.com/ericlippert/archive/2009/05/07/zip-me-up.aspx</a></p> <p>It's especially interesting because he's posted the source for the new extension in C#4:</p> <pre><code>public static IEnumerable<TResult> Zip<TFirst, TSecond, TResult> (this IEnumerable<TFirst> first, IEnumerable<TSecond> second, Func<TFirst, TSecond, TResult> resultSelector) { if (first == null) throw new ArgumentNullException("first"); if (second == null) throw new ArgumentNullException("second"); if (resultSelector == null) throw new ArgumentNullException("resultSelector"); return ZipIterator(first, second, resultSelector); } private static IEnumerable<TResult> ZipIterator<TFirst, TSecond, TResult> (IEnumerable<TFirst> first, IEnumerable<TSecond> second, Func<TFirst, TSecond, TResult> resultSelector) { using (IEnumerator<TFirst> e1 = first.GetEnumerator()) using (IEnumerator<TSecond> e2 = second.GetEnumerator()) while (e1.MoveNext() && e2.MoveNext()) yield return resultSelector(e1.Current, e2.Current); } </code></pre> <hr> <p><strong>Original answer:</strong></p> <p>Are you referring to a join?</p> <pre><code>from x in seq1 join y in seq2 on x.foo equals y.foo select new {x, y} </code></pre> <p>There is also pLinq - which executes linq statements in parallel (across multiple threads).</p> <hr> <p><strong>Edit:</strong></p> <p>Ah - thanks for clarifying the question, though I really don't think my answer deserved a vote down.</p> <p>It sounds like what you want is something like:</p> <pre><code>from x in seq1 join y in seq2 on x.Index equals y.Index select new {x.Foo, y.Bar} </code></pre> <p>Unfortunately you can't do that with Linq - it extends <code>IEnumerable</code>, which only really has <code>current</code> and <code>next</code> properties, so no index property.</p> <p>Obviously you can do this easily in C# with a nested for-loop and an if block, but you can't with Linq I'm afraid.</p> <p>The only way to mimic this in linq syntax is to artificially add the index:</p> <pre><code>int counter = 0; var indexed1 = ( from x in seq1 select { item = x, index = counter++ } ).ToList(); //note the .ToList forces execution, this won't work if lazy counter = 0; var indexed2 = ( from x in seq2 select { item = x, index = counter++ } ).ToList(); var result = from x in indexed1 join y in indexed2 on x.index = y.index select new {x.item.Foo, y.item.Bar} </code></pre>

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