quarto rmarkdown code block to only display certain lines

Question

I have a .qmd / .rmd file that wants to show the output of block of code. The code block has a lot of lines at the beginning that I'd like to hide, in the example below I'd like the output to be the third line of code str(month) and output the result of str(month). I've attempted to edit the code block parameters, but it's giving me an error:

---
format:
  html: default
---

```{r}
#| echo: c(3)
month <- "July"

str(month)
```

Error:

7: #| echo: c(3)
            ~~~
8: month <- "July"
x The value c(3) is string.
i The error happened in location echo.

rmarkdown support files suggest something like this might be possible

Why not just put the lines you want to hide in another chunk with `echo=FALSE` set? Code chunks are just formatting/organisational elements so there doesn't seem to be any use case where lines you want to echo and lines you don't *have* to be evaluated together in one chunk. — Joe Roe, May 12 '22 at 15:56
this is certainly true, but I'm finding it easier to keep my code all in one place rather than splitting it across chunks — pluke, May 12 '22 at 16:34

Lucca Nielsen · Answer 1 · 2022-05-12T15:12:00.303

1

I don't know if I understood the question correctly. But you can choose to display only the code you want based on the index of the line inside specific chunk. Insert the number of index line you want to show inside the c() {r, echo = c()}

Your specific case

---
format:
  html: default
---

```{r, echo = c(2)}
month <- "July"
str(month) # line 2
```

Other Example:

---
format:
  html: default
---

```{r, echo = c(5,8)}
# Hide
month <- "July"

## Show code and output
str(month) # Line 5

## Show code and output
1+1 # Line 8

## Show just output
2+2

```

edited May 12 '22 at 15:12

answered May 12 '22 at 15:01

Lucca Nielsen

1,497
3
16

many thanks, this works inline in the `{r, echo = c(2)}` header perfectly. It also works as part of the code chunk body, using `#| echo = c(2)` rather than `#| echo: c(2)`. Does anyone know why? `:` assignment seems to be the normal way to pass parameters in the code chunk body – pluke May 12 '22 at 16:32

score 1 · Accepted Answer · answered May 13 '22 at 09:39

This does not work because you are using YAML syntax for chunk options as recommended with Quarto but #| echo: c(3) is not valid YAML. #| echo: 3 is.

You can use !expr within YAML field to parse R code if necessary. #| echo: !expr c(3) would work. It is explained here: https://quarto.org/docs/computations/r.html#chunk-options

However, know that knitr supports other way to specify chunk options:

Usual header where option needs to be valid R code

```{r, echo = c(3)}
#| echo: c(3)
month <- "July"

str(month)
```

And a multiline version of it, useful when having long option like fig.cap

```{r}
#| rmdworkflow,
#| echo = FALSE,
#| fig.cap = "A diagram illustrating how an R Markdown document
#|   is converted to the final output document.",
#| out.width = "100%"

knitr::include_graphics("images/workflow.png", dpi = NA)
```

See the announced in blog post for more about this new syntax: https://yihui.org/en/2022/01/knitr-news/

This question has also been asked in Github - so more detailed answer there: https://github.com/quarto-dev/quarto-cli/issues/863

quarto rmarkdown code block to only display certain lines

2 Answers2