How to save a variable in memory?

[Tungill]

Hello!
Context: I have a tracker where I add a new data point every time I spend time studying a language. I have a function that automatically counts every consecutive day I studied by aggregating the inputs of the tracker on a Day period, then filtering to ignore every data points before the last time I didn't study at all for a day (0 data).
Need: I would like to be able to save my "Best Consecutive Streak" on a variable to display it on the App. So if some day I start my streak over, I have memory of my personal score to beat.

Is there a way currently to save a variable separately from a function?

As a test, I tried to have a custom lua function derived from "Total This Period" where I compare current_streak with higher_streak and if current_streak > higher_streak then higher_streak = current_streak
My issue is that I'm forced to initiate the local higher_streak = 0 otherwise it shows an "attempt to compare __It on nil and number" on the lua function display. And by doing this, every new day, the variable reset to "0".

Any idea / similar case on your hands?

[SamAmco]

Hi. You do not actually need persistent state for this. You can use a function for example that always returns one data point containing the longest streak of all time. For example:

  local core = require("tng.core")

  return function(source)
      local emitted = false

      -- Source data points are reverse chronological, so collect them first.
      local points = source.dpall()

      local current_streak = 0
      local best_streak = 0
      local newest_point = points[1]

      -- Walk oldest -> newest.
      for i = #points, 1, -1 do
          local dp = points[i]

          if dp.value and dp.value > 0 then
              current_streak = current_streak + 1
              if current_streak > best_streak then
                  best_streak = current_streak
              end
          else
              current_streak = 0
          end
      end

      return function()
          if emitted then return nil end
          emitted = true

          if newest_point then
              return {
                  timestamp = newest_point.timestamp,
                  offset = newest_point.offset,
                  value = best_streak,
                  label = "Best streak"
              }
          end

          return {
              timestamp = core.time().timestamp,
              value = 0,
              label = "Best streak"
          }
      end
  end

[Tungill]

Does it react as you wanted? When I use the new function under aggregation (1) the result (2) doesn't return a unique data point like in the function you manually wrote above (3).
This is what I'm tracking on the screenshot you see below (4): A standard tracker every time I consume media in that language. There is a lot of data point because I watch a lot of small content throughout the same day.
(1) Function graph using in-app Best Streak function
(2) Using in-app Best Streak function
(3) Using manual script function
(4) Data Source tracked

[Tungill]

It seems your function would be best suited if I track a daily sum, instead of directly every small entry. I should be able to do that with the aggregation function.
EDIT: Yep, it works best when I do a previous aggregation function, then pass it through this function.

But I'm curious how does it handle an empty day? Should I need to explicitly write an empty day as a Data point with value = 0 ? Or does it detect an empty day with no entry between 2 dates?
I believe it can not right? Since it doesn't compare timestamps between two data points.

[SamAmco]

Hey, yeah that looks like what i was intending. I did change it a little. I figured you probably want to chain it with a daily total in your case, but i assume there are use cases where you might not want that, so best to keep it targeted and composable. Daily sum based aggregation would put a 0 data point on any day with no data points. The function i published gives you a running best streak so you know what your best streak was at any given point in history. I assume this is more flexible/helpful. The top data point is always your best streak to date, you should be able to just put that on a card using the "LastValue" graph type if needed, or you could draw a graph of how/when your best streak changed.

[Tungill]

Ah, that's what I was wondering. Nice then if the Daily aggregation does this.
Yeah, you're probably right! It's better to be able to retrieve any info from past streaks. That's the good part about your design, is that I can rearrange anything anytime, it doesn't matter as long as I keep the tracking data point history.

[Tungill]

I'll try LastValue. It seems to be fine right now.