Q:

Group by array contents

I have a List<Tuple<string,long,byte[]>> and I want to group by the contents of the byte array.
Is there a simple way to do this with GroupBy and a lambda?
Ideally, I want to do this without creating an intermediate data structure (like a string to hold the elements of the array).

A:

You can achieve that using custom IEqualityComparer<byte[]> (or even better, generic one: IEqualityComparer<T[]>) implementation:
class ArrayComparer<T> : IEqualityComparer<T[]>
{
    public bool Equals(T[] x, T[] y)
    {
        return x.SequenceEqual(y);
    }

    public int GetHashCode(T[] obj)
    {
        return obj.Aggregate(string.Empty, (s, i) => s + i.GetHashCode(), s => s.GetHashCode());
    }
}

I'm pretty sure GetHashCode could be implemented much better, but it's just an example!
Usage:
var grouped = source.GroupBy(i => i.Item3, new ArrayComparer<byte>())

