How to render an R document with Quarto

Quarto combines prose and executable R in one .qmd source, then turns the evaluated document into a shareable output format. Rendering from the command line makes the same report repeatable outside an editor or interactive R session.

An inline R expression places a computed value inside a sentence without displaying a separate code cell. Because the source contains only inline code, the engine: knitr field explicitly selects R execution for the document.

The source requires working Quarto and R installations plus the rmarkdown and knitr R packages. Installing rmarkdown from CRAN also installs knitr; no external input file is needed. Success means quarto render creates report.html and the rendered file contains the computed mean fuel economy of 20.09 mpg.

1. Confirm that the rmarkdown and knitr namespaces load for Quarto's Knitr engine.

   $ Rscript -e 'invisible(lapply(c("rmarkdown", "knitr"), loadNamespace))'

2. Create report.qmd with HTML metadata and opening text.

   report.qmd

   ---
   title: "Motor trend summary"
   format: html
   engine: knitr
   ---
    
   The report calculates a summary from the built-in `mtcars` data.

3. Add the inline R expression after the opening text.

   report.qmd

   Mean fuel economy: `{r} round(mean(mtcars$mpg), 2)` mpg.

   The expression starts with `{r} and ends at the next backtick. The built-in mtcars data keeps the calculation independent of external files and packages.

4. Review the completed source.

   report.qmd

   ---
   title: "Motor trend summary"
   format: html
   engine: knitr
   ---
    
   The report calculates a summary from the built-in `mtcars` data.
   
   Mean fuel economy: `{r} round(mean(mtcars$mpg), 2)` mpg.

5. Render the document from its working directory.

   $ quarto render report.qmd
   processing file: report.qmd
   1/1
   output file: report.knit.md
   
   ##### snipped #####
   
   Output created: report.html

   The input path report.qmd belongs first. Quarto uses the HTML format declared in the document and writes report.html beside the source file.

6. Confirm that the generated HTML contains the evaluated R result.

   $ quarto pandoc report.html --to plain
   Motor trend summary
   
   The report calculates a summary from the built-in mtcars data.
   
   Mean fuel economy: 20.09 mpg.

   The metric and 20.09 value must appear in text extracted from report.html. A missing value means the R expression did not produce the promised report content.