ThreeZip.linq.cs

void Main()
{
    var list1 = Enumerable.Range(0, 10000).Select(i => i.ToString());
    var list2 = Enumerable.Range(0, 10000).Select(i => i.ToString());
    var list3 = Enumerable.Range(0, 10000).Select(i => i.ToString());
    
    // First run to avoid JIT during the benchmark
    list1.ZipOne(list2, list3, Merge).Count();
    list1.ZipTwo(list2, list3, Merge).Count();
    
    var stopWatch = new Stopwatch();
    
    TimeSpan t1;
    TimeSpan t2;
    
    // declared as int rather than object to avoid boxing
    int result;
    
    stopWatch.Start();
    
    for(var i = 0; i < 1000; i++)
        result = list1.ZipOne(list2, list3, Merge).Count();
    
    stopWatch.Stop();
    t1 = stopWatch.Elapsed.Dump("ZipOne");
    
    stopWatch.Restart();
    
    for(var i = 0; i < 1000; i++)
        result = list2.ZipTwo(list2, list3, Merge).Count();
    stopWatch.Stop();
    t2 = stopWatch.Elapsed.Dump("ZipTwo");
    
    var difference = Math.Abs(t1.Subtract(t2).TotalMilliseconds);
    var average = t1.Add(t2).TotalMilliseconds / 2;
    (difference / average * 100).Dump("Difference");
}

public object Merge(string s1, string s2, string s3)
{
    return new { s1, s2, s3 };
}

// Define other methods and classes here
public static class EnumerableExtensions
{
    public static IEnumerable<TResult> ZipOne<TFirst, TSecond, TThird, TResult>(
        this IEnumerable<TFirst> first,
        IEnumerable<TSecond> second,
        IEnumerable<TThird> third,
        Func<TFirst, TSecond, TThird, TResult> resultSelector )
    {
        if( first == null )
            throw new ArgumentNullException( "first cannot be null" );
        if( second == null )
            throw new ArgumentNullException( "second cannot be null" );
        if( third == null )
            throw new ArgumentNullException( "third cannot be null" );
        if(resultSelector == null)
            throw new ArgumentNullException( "resultSelector cannot be null" );

        using ( var iterator1 = first.GetEnumerator() )
        using ( var iterator2 = second.GetEnumerator() )
        using ( var iterator3 = third.GetEnumerator() )
        {
            while ( iterator1.MoveNext() && iterator2.MoveNext() && iterator3.MoveNext() )
            {
                yield return resultSelector(
                    iterator1.Current,
                    iterator2.Current,
                    iterator3.Current );
            }
        }
    }
    
    public static IEnumerable<TResult> ZipTwo<TFirst, TSecond, TThird, TResult>(
    this IEnumerable<TFirst> first,
    IEnumerable<TSecond> second,
    IEnumerable<TThird> third,
    Func<TFirst, TSecond, TThird, TResult> resultSelector)
    {
        return first.Zip(second, (f, s) => new { f, s })
                    .Zip(third, (fs, t) => resultSelector(fs.f, fs.s, t));
    }
}

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