Alluvial, not Sankey. How should the input data be structured to create a flow chart?

[aourednik]

This package seems designed to produce alluvial plots, not Sankey diagrams.

See e.g.:
https://www.analyticsvidhya.com/blog/2022/06/data-visualisation-alluvial-diagram-vs-sankey-diagram/

Using the mtcars example data and applying the make_long transformation strongly suggests that the main purpose of this package is to study multidimensional categorial data.
The "riverplot" package for R, available on CRAN, makes actual Sankeys.
Of course, your package could also be used to show flows (processes), but more documentation would be needed to use it fo this purpose. Could you add this?
Would be helpful, since your pacakge integartes better with ggplot2 than riverplot does

Best,
A.