Is there a zip-like method in .Net?

Question

In Python there is a really neat function called zip which can be used to iterate through two lists at the same time:

list1 = [1, 2, 3]
list2 = ["a", "b", "c"]
for v1, v2 in zip(list1, list2):
    print v1 + " " + v2

The above code shoul produce the following:

1 a
2 b
3 c

I wonder if there is a method like it available in .Net? I'm thinking about writing it myself, but there is no point if it's already available.

Answer 1

Nope, there is no such function in .NET. You have roll out your own. Note that C# doesn't support tuples, so python-like syntax sugar is missing too.

You can use something like this:

class Pair<T1, T2>
{
    public T1 First { get; set;}
    public T2 Second { get; set;}
}

static IEnumerable<Pair<T1, T2>> Zip<T1, T2>(IEnumerable<T1> first, IEnumerable<T2> second)
{
    if (first.Count() != second.Count())
        throw new ArgumentException("Blah blah");

    using (IEnumerator<T1> e1 = first.GetEnumerator())
    using (IEnumerator<T2> e2 = second.GetEnumerator())
    {
        while (e1.MoveNext() && e2.MoveNext())
        {
            yield return new Pair<T1, T2>() {First = e1.Current, Second = e2.Current};
        }
    }
}

...

var ints = new int[] {1, 2, 3};
var strings = new string[] {"A", "B", "C"};

foreach (var pair in Zip(ints, strings))
{
    Console.WriteLine(pair.First + ":" + pair.Second);
}

Answer 2

Update: It will be built-in in C# 4!

Here is a C# 3 version:

IEnumerable<TResult> Zip<TResult,T1,T2>
    (IEnumerable<T1> a,
     IEnumerable<T2> b,
     Func<T1,T2,TResult> combine)
{
    using (var f = a.GetEnumerator())
    using (var s = b.GetEnumerator())
    {
        while (f.MoveNext() && s.MoveNext())
            yield return combine(f.Current, s.Current);
    }
}

Dropped the C# 2 version as it was showing its age.

Answer 3

As far as I know there is not. I wrote one for myself (as well as a few other useful extensions and put them in a project called NExtension on Codeplex.

Apparently the Parallel extensions for .NET have a Zip function.

Here's a simplified version from NExtension (but please check it out for more useful extension methods):

public static IEnumerable<TResult> Zip<T1, T2, TResult>(this IEnumerable<T1> source1, IEnumerable<T2> source2, Func<T1, T2, TResult> combine)
{
    using (IEnumerator<T1> data1 = source1.GetEnumerator())
    using (IEnumerator<T2> data2 = source2.GetEnumerator())
        while (data1.MoveNext() && data2.MoveNext())
        {
            yield return combine(data1.Current, data2.Current);
        }
}

Usage:

int[] list1 = new int[] {1, 2, 3};
string[] list2 = new string[] {"a", "b", "c"};

foreach (var result in list1.Zip(list2, (i, s) => i.ToString() + " " + s))
    Console.WriteLine(result);

Answer 4

There's also one in F#:

let zipped = Seq.zip firstEnumeration secondEnumation

Answer 5

That's a really cool function. I've never seen it before (I've never worked with Python or F#). Out of curiousity, what happens if the two lists are different lengths?