How to iterate through two IEnumerables simultaneously?

c# iteration ienumerable
Danvil picture Danvil · Apr 27, 2010 · Viewed 14k times · Source

I have two enumerables: IEnumerable<A> list1 and IEnumerable<B> list2. I would like to iterate through them simultaneously like:

foreach((a, b) in (list1, list2))
{
    // use a and b
}

If they don't contain the same number of elements, an exception should be thrown.

What is the best way to do this?

Answer

Jon Skeet picture Jon Skeet · Apr 27, 2010

You want something like the Zip LINQ operator - but the version in .NET 4 always just truncates when either sequence finishes.

The MoreLINQ implementation has an EquiZip method which will throw an InvalidOperationException instead.

var zipped = list1.EquiZip(list2, (a, b) => new { a, b });

foreach (var element in zipped)
{
    // use element.a and element.b
}

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