Cross-referencing panels inside a figure created all together (e.g., with gridExtra::grid.arrange)

[dmkaplan2000]

Description

I have multi-panel figures created in a quarto document using gridExtra::grid.arrange and I want to cross-reference the panels in the figure. For example, if I have the following code:

:::{#fig-myfig}
```{r}
df = data.frame(id=rep(c("(a) Line","(b) Parabola"),each=5),
                x = rep(-2:2,2), y = c(-2:2,(-2:2)^2))
library(ggplot2)
ggplot(df,aes(x,y)) + geom_line() + facet_wrap(vars(id))
```

A figure with multiple panels.
:::

Then I want to include in the document a cross-reference of the sort "Figure 1a". To reference the entire figure, I would put @fig-myfig so I would want to do something like @fig-myfiga, but of course that doesn't work as it doesn't recognize the a as being separate from myfig. I tried using the notation suggested in the quarto documentation of @fig-myfig-1, but this only works if quarto assembles the figure panels with subcaptions. For many reasons it is much easier for me to let gridExtra::grid.arrange or facet_wrap do the assembling. The only partial solutions I have found is to do @fig-myfig a or @fig-myfig(a), but neither of these is the desired notation for figure panels. I also tried tricking quarto into separating myfig from a, for example doing @fig-myfig``a, but these tricks failed or didn't produce what I wanted.

Is there a better way to achieve what I want?

[mcanouil]

If you combine the plots, there are no subfigures, thus Quarto cannot cross-reference what does not exist.

See:

• https://quarto.org/docs/authoring/cross-references-divs.html#subreferences
• https://quarto.org/docs/reference/cells/cells-knitr.html#figures

---
title: "Quarto Playground"
format: html
---

```{r}
#| label: fig-myfig
#| fig-cap: A figure with multiple panels.
#| fig-subcap: true
#| layout-ncol: 2
df <- data.frame(
  id = rep(c("(a) Line", "(b) Parabola"), each = 5),
  x = rep(-2:2, 2),
  y = c(-2:2, (-2:2)^2)
)
library(ggplot2)
for (iid in unique(df[["id"]])) {
  print(
    ggplot(subset(df, id == iid)) +
      aes(x = x, y = y) +
      geom_line()
  )
}
```

[dmkaplan2000]

And to be clear, your solution would work in many cases, but in my specific case, it would be impossible or impractical for various reasons (I am using rather complex panel placement, legends, etc.).

[mcanouil]

it would be impossible or impractical for various reasons (I am using rather complex panel placement, legends, etc.)

Well, maybe but layout can achieve "rather complex panel placement".

---
title: "Quarto Playground"
format: html
---

```{r}
#| label: fig-myfig
#| fig-cap: A figure with multiple panels.
#| fig-subcap: true
#| layout: [[1, 1], [1], [2, 1]]
df <- data.frame(
  id = rep(LETTERS[1:5], each = 5),
  x = rep(-2:2, 5),
  y = c(-2:2, (-2:2)^2, (-2:2)^3, (-2:2)^4, (-2:2)^5)
)
library(ggplot2)
for (iid in unique(df[["id"]])) {
  print(
    ggplot(subset(df, id == iid)) +
      aes(x = x, y = y) +
      geom_line()
  )
}
```

[dmkaplan2000]

I get it, but how can I create the text "Fig. 1a" if I cannot put the a next to @fig-myfig without screwing up the cross-reference? That is my question more than anything, is there some way to tell quarto where the cross-reference ends without changing the final visual output? For example, in bash, when there is some risk of confusion regarding the extent of a shell variable, you can surround it in {} (e.g., ${HOME}abc is valid, but $HOMEabc is not). Is there an equivalent for quarto?

[mcanouil]

For example, in bash, when there is some risk of confusion regarding the extent of a shell variable, you can surround it in {} (e.g., ${HOME}abc is valid, but $HOMEabc is not). Is there an equivalent for quarto?

No and I am pretty confident, it is not going to happen this way.

The only syntax that would make sense would be the one used by citeproc for references:

See https://quarto.org/docs/authoring/footnotes-and-citations.html.

(It is not supported, cc @cscheid )

---
title: "Quarto Playground"
format: html
---

::: {#fig-myfig}
Figure

Content
:::

[@fig-myfig, a]

[dmkaplan2000]

This syntax seems interesting, but that notation for bibtex citations is really doing a different task I think, making it not particularly suitable in this use case in my view (but perhaps I am mistaken). In general, it would seem useful to be able to place something other than a space or a punctuation mark besides a cross-reference (as an aside, I tried @fig-myfig.a and this also failed). It is a really neat feature of quarto that you can often do paneling using quarto, but I think there will always be cases where quarto paneling isn't quite what you want, and ideally quarto should not be forcing users not to use very effective approaches to paneling that already exist in R.

[mcanouil]

The comma is not a separator.
Look at the link I shared for articles citation and the syntax.

as an aside, I tried @fig-myfig.a and this also failed)

You can try a lot of other stuff, none of them will work. As I said, Quarto can only cross-reference "float objects" and only article citation supports (via Pandoc) some customisation of how you cite them.

[dmkaplan2000]

Perhaps there is some subtlety to how citeproc citations work that I am not aware of, but doesn't the comma become part of the output text, which is not what I am looking for (i.e., [@fig-myfig, a] would become "Figure 1, a", not "Figure 1a")? In any case, if this syntax could be made to work, then I am all for it. I wasn't proposing a specific solution based on what is done in bash or citeproc or anything else.

And in response to your next comment, I wasn't trying to get quarto to handle my cross-reference to a subpanel, I was just trying get the "a" adjacent to "Figure 1" in a somewhat natural way (e.g., without a strange space). I thought "." might work as a separator, but it didn't. I have moved on...

[mcanouil]

[@fig-myfig, a] this was only a rough example.
The syntax described in the link I shared is:

Anyhow, what you are asking is not currently possible and I am afraid it won't be soon.
I believe, the following might be of interest to you:

• Custom Cross-Reference Type in a book: is there a way to associate each reference with a custom label? #8034