I think I have worked it out partially,
I didn’t realise you could store lists as complex objects within attributes, I thought they could only be simple singular objects (you can’t store arrays, but lists and dict objects are acceptable).
So for my sensor, there would be three attributes: datetime-list; rain-list; and precipitation-list. Each time I refresh, the data received (three datasets) would be split into 3 and stored as three list-formatted attributes.
Now I just need to work out how I put that data into an ApexChartt, such that the attribute datetime-list is x axis and rain-list is y axis, so creating a time series chart I want. I can see you had this conversation in this thread: How to draw curve/ graph card with own values, not sensor values? - #13 by vingerha using plotly, where you can define the data on the x and y axis independently not rely on stating an entity to plot). Can you do the same with Apex and state the x axis values as I can’t see it on the GitHub README?
Does that make sense?
(NB with regard to changing the retention period for this sensor, it doesn’t seem you can, but you can create a service call to purge a single entitiy via the Recorder service I think)