寓言中的和解耗尽了 RAM

Question

I am trying to use forecast reconciliation in fable to improve forecasts at low, intermittent hierarchy levels. However, my computer runs out of memory for anything but trivial examples.

I am basing my analysis on example code from the presentation "Tidy Time Series & Forecasting in R : 10. Forecast Reconciliation" (bit.ly/fable2020, presented at rstudio::conf 2020) :

tourism %>%
  aggregate_key(Purpose * (State / Region), Trips = sum(Trips)) %>%
  model(ets = ETS(Tripsl)) %>%
  reconcile(ets_adjusted = min_trace(ets)) %>%
  forecast(h = 2)

This runs fine, even on my 8 GB RAM laptop.

However, our data has many more hieriarchy levels and groupings than this example, and the code is never able to complete. As a reproducible example I have added more three dummy levels to the "tsibble::tourism" dataset and include these in the aggregate_key . This runs out of memory even on my 50 GB RAM server!

tourism %>% mutate(Region1 = Region, Region2 = Region, Region3 = Region) %>% 
  aggregate_key(Purpose * (State / Region/ Region1 / Region2 / Region3), Trips = sum(Trips)) %>%
  model(ets = ETS(Trips)) %>%
  reconcile(ets_adjusted = min_trace(ets)) %>%
  forecast(h = 2)

Error: cannot allocate vector of size 929 Kb

Question Is there some way I can run this without reducing hierarchy levels and without running out of memory? Thanks!

Answer 1

Thanks for your interest in fable. In the current CRAN version of fabletools (0.1.2) reconciliation is experimental, and as part of we have prioritised interface design/experimentation over performance.

As part of this experimentation, we are trying to find new ways to flexibly identify the aggregation structure and build an appropriate summation matrix. Seemingly the current approach is not ideal for deep nesting of series as your example points out.

I've written an alternate algorithm which I think performs better in these circumstances, both in terms of time and space complexity. This should allow you to compute hierarchical forecasts without using too much memory.

Update: This change is now published in version 0.1.3 of fabletools.