1-linq-list-to-dictionary.cs

var result = List.Select((x, i) => new { Key = i, Value = x }).ToDictionary(x => x.Key, x => x.Value);

2-rx-linq-syntax.cs

// IObservable<byte> (socket.Receiver) to IObservable<string> (Receiver)

Receiver = from header in socket.Receiver.Buffer(sizeof(int))
                       let length = BitConverter.ToInt32(header.ToArray(), 0)
                       let body = socket.Receiver.Take(length)
                       select encoding.GetString(body.ToEnumerable().ToArray());

3-rx-linq-syntax-with-exception-handling.cs

// Syntax with exception handling
// IObservable<byte> (socket.Receiver) to IObservable<string> (Receiver)

Receiver = socket.Receiver.Buffer(sizeof(int))
                .Select(header =>
                    {
                        try
                        {
                            var length = BitConverter.ToInt32(header.ToArray(), 0);
                            var body = socket.Receiver.Take(length);
                            return body;
                        }
                        catch (Exception ex)
                        {
                            Debug.WriteLine(ex);
                            return Observable.Empty<byte>();
                        }
                    })
                .Select(body =>
                {
                    return encoding.GetString(body.ToEnumerable().ToArray());
                });