`tidymodels` and panel data, postprocessing, multiple outcomes

[dajmcdon]

This is a long-term question / tracking.

As we continue to iterate on epipredict, it is becoming increasingly clear that we are implementing this framework not just for epidemiological data, but for general panel data along with other bells and whistles. One can imagine simply wanting to use tidymodels with panel data, and epipredict/epiprocess provides a framework to do so: convert your data to an epi_df, then use an epi_workflow rather than a workflows::workflow.

1. At minimum, we should demonstrate this with a vignette.
2. Down stream, we should consider whether to strip out some bits of epipredict and try to incorporate directly into tidymodels.

• The panel data request has been around for a while but is not a priority.
• Neither is postprocessing predictions: Post-processing tidymodels/workflows#154 predictions.
• Neither is prediction of multiple outcomes simultaneously: Multi predict? tidymodels/workflows#4