This forum is specifically for questions about Tectonic, are you sure that you have a question about Tectonic, and not about LaTeX in general? In the latter case, asking your question at a site like https://tex.stackexchange.com will get you a lot more response.
As to your question, I’m sure something like that must have been asked before on the site I mentioned, e.g. https://tex.stackexchange.com/questions/152027/plot-data-from-a-latex-table, although I don’t see why you cannot have your data in a separate file.