Extend Aggregate / Scan Functions to have more than 1 value of history of input and output

[mattpodwysocki]

Extend Aggregate / Scan Functions to have more than 1 value of history of input and output

[mattpodwysocki]

andresier wrote Jan 27 at 7:45 AM

Have you considered using a Tuple type structure to achieve this yourself?
e.g. Tuple<T, T>
Your scan function could promote the previous update into the first item, and your current item into the 2nd.
If you want to hold more, simply change the Scan to use Tuple<T, T, T....> and create a new Tuple each scan but with the items shifted along.

Just an idea, in case you had not considered it - because it is relatively simple to achieve this yourself.

[mattpodwysocki]

sirinath wrote Jan 27 at 8:10 AM

I raised this with the exception that this change would be replicated in other ports where there no tuple type. E.g. RxJava.

The tuple solution would be confined to the .net and a few other ports.

[mattpodwysocki]

andresier wrote Jan 27 at 10:35 AM

Tuple was an example (one I have used for something similar), but you could create your own alternative or simply use an array. It doesn't sound right to change the method signature of Scan to handle this.
Here is an example with array. It is written in C#, but I'm sure you can port it to Java.

Something like this (untested - just hand cranked it now):

source...
.Scan(new int[3], (a, b) => {
    return new int[] { a[1], a[2], b };
})

Should produce an array each time, whereby you have the most recent 3 values.

[mattpodwysocki]

sirinath wrote Jan 27 at 11:36 AM

This is fine. If you give a option to get n input and m output values the implementation may be more efficient.

The above will create a object each time it is evoked. Also if you want both input and output this becomes awkward as you need to keep a input data structure and output data structure.