Feature request: For quarto book qmd files, allow execution order to differ from order appearing in book

[donboyd5]

I have the following common use case:

• writing a report with many qmd chapters
• each chapter calculates key facts (in R)
• up-front summary chapter reprises key facts in text with inline code and perhaps includes a summary table

Thus, I need to calculate the facts in the body-of-the-report chapters before executing the code for the summary chapter, but I want the summary to appear first. It would be great to define an execution order for the files and an appearance order for the files that may be different, so that I could calculate the summary chapter last but have it appear first.

There are workarounds, of course, such as:

• Calculate everything first - for example, R files executed at the start that do all calculations, and the qmd files merely report the results (tables, figures, inline text). But this makes for a potentially awkward and error-prone workflow as it requires thinking about the whole project and its presentation separately. A more-natural workflow (for me) is to develop the calculations at the same time and in the same place that I am figuring out how to present the information.
• Have every full execution create and save results into a prior-results folder. In the next execution these results will be available to the summary chapter at the start. Requires being extra-careful that the results have not changed from one execution to the next, or putting in error checking to be sure that, after all files are executed, the current results are the same as prior results.

Neither of these seems as good as having the ability to separate execution order from appearance order.

Would love to hear if there are better workarounds - or perhaps quarto already has this capability and I haven't found it yet.

Many thanks.

[rgaiacs]

Dear @donboyd5, I have the same use case.

Quarto Document

If you are only targeting HTML output, one great tool is Observable as it build a graph of dependency before execute the code. This allows you to calculate key facts in R, export to Observable and customise the appearance with Observable.

Zip file with minimal working example

Consider

---
title: "Minimal Working Example"
---

# Summary

Key fact is ${key_fact}

# Methods

```{r}
key_fact <- 1 + 1
ojs_define(key_fact = key_fact)

It produces

![Screenshot 2022-12-07 at 11-53-38 Minimal Working Example](https://user-images.githubusercontent.com/1506457/206084480-4809646b-6705-445c-abd6-22be432e5618.png)

Observable is injecting `key_fact`.

If you are targeting PDF or DOCX, Observable will not work. :cry: You are limited to the workarounds that you mentioned.

# Quarto Book

AFAIK, Observable will not work across chapters. :cry: 

[Zip file with minimal working example](https://github.com/quarto-dev/quarto-cli/files/10172663/ojs-book.zip)

One chapter with

Summary

1 + 1

Key fact is ${key_fact}

and another chapter with

Methods

key_fact <- 1 + 1
ojs_define(key_fact = key_fact)

produces

![Screenshot 2022-12-07 at 11-59-02 Minimal Working Example](https://user-images.githubusercontent.com/1506457/206085190-ff3ee955-4555-4a0f-ab7e-d2253d6b155b.png)

Observable silent fail to inject `key_fact` because the variable was defined in another file.

[donboyd5]

Thank you, @rgaiacs. I did not know about this. I have been experimenting with it. It seems very useful for situations in which I need to pull information forward within a single qmd file. Meanwhile, I'll hope over the longer term differing execution and appearance orders may be added as a feature.

Also, thanks for the reproducible example - allowed me to get up and running quickly.

[nickdickinson]

@donboyd5 Have you considered using quarto includes: https://quarto.org/docs/authoring/includes.html

I haven't myself but I read that it should also deal with this specific use case: "For example, here we include a .qmd that does some data preprocessing that we want shared across multiple documents"