Pair-wise iteration in C# or sliding window enumerator

c# .net iterator ienumerable
f3lix picture f3lix · Feb 23, 2009 · Viewed 14k times · Source

If I have an IEnumerable like:

string[] items = new string[] { "a", "b", "c", "d" };

I would like to loop thru all the pairs of consecutive items (sliding window of size 2). Which would be 

("a","b"), ("b", "c"), ("c", "d")

My solution was is this 

    public static IEnumerable<Pair<T, T>> Pairs(IEnumerable<T> enumerable) {
        IEnumerator<T> e = enumerable.GetEnumerator(); e.MoveNext();
        T current = e.Current;
        while ( e.MoveNext() ) {
            T next = e.Current;
            yield return new Pair<T, T>(current, next);
            current = next;
        }
    }

 // used like this :
 foreach (Pair<String,String> pair in IterTools<String>.Pairs(items)) {
    System.Out.PrintLine("{0}, {1}", pair.First, pair.Second)
 }

When I wrote this code, I wondered if there are already functions in the .NET framework that do the same thing and do it not just for pairs but for any size tuples. IMHO there should be a nice way to do this kind of sliding window operations.

I use C# 2.0 and I can imagine that with C# 3.0 (w/ LINQ) there are more (and nicer) ways to do this, but I'm primarily interested in C# 2.0 solutions. Though, I will also appreciate C# 3.0 solutions.

Answer

Ian Mercer picture Ian Mercer · Aug 2, 2010

In .NET 4 this becomes even easier:-

var input = new[] { "a", "b", "c", "d", "e", "f" };
var result = input.Zip(input.Skip(1), (a, b) => Tuple.Create(a, b));

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