Kapacitor Lambda Mean

I am trying to generate baseline with Kapacitor batch|query by querying the same interval from InfluxDB 1, 2, 3 and 4 weeks ago, then shifting it forward and joining together like this:

var w1 = batch
    |query('SELECT mean(""value"") FROM ""MyDB"".""autogen"".""MetricName""')
        .offset(1w).period(period).every(1m).align().groupBy(time(1m))
    |shift(1w)

var w2 = batch
    |query('SELECT mean(""value"") FROM ""MyDB"".""autogen"".""MetricName""')
        .offset(2w).period(period).every(1m).align().groupBy(time(1m))
    |shift(2w)

var w3 = batch
    |query('SELECT mean(""value"") FROM ""MyDB"".""autogen"".""MetricName""')
        .offset(3w).period(period).every(1m).align().groupBy(time(1m))
    |shift(3w)

var w4 = batch
    |query('SELECT mean(""value"") FROM ""MyDB"".""autogen"".""MetricName""')
        .offset(4w).period(period).every(1m).align().groupBy(time(1m))
    |shift(4w)

var bj = w1
    |join(w2, w3, w3)
        .as('w1', 'w2', 'w3', 'w4')
        .fill('null')

var b = bj
    |eval(lambda: (""w1.mean"" + ""w2.mean"" + ""w3.mean"" + ""w4.mean"") / float(4.0))
        .as('avg')

I am using Full Outer Join, since some weeks may be missing a value, in which case I would calculate baseline as mean of 3 present values.

However it appears that lambda doesn't support Mean() or any such mathematical functions. It also seem to not support checks for null values.

Is there a way to calculate baseline like this?

Also once the baseline is calculated, how is it possible to keep it cached so that incoming stream data may be checked against baseline?

Any help is appreciated! Thank you

I ended up creating a UDF using C# .NET Core running as a process side by side, querying InfluxDB, doing math and caching the results.