Centering incomplete when using subfig in markdown with out.width < "100%"

[slrellison]

Using subfig as in bookdown 6.6, with fig.ncol=1, fig.align="center" and out.width="80%" (for example), the final subfigure is not aligned with previous figures.

Inspection of the LaTeX shows that this is due to a missing \newline after the final subfigure; inserting it manually in the LaTeX output corrects the alignment.

Reprex based on section 6.6 example:

---
output: 
  pdf_document:
    extra_dependencies: "subfig"
    keep_tex: yes
---

```{r, fig.cap='Figure 1', fig.dim=c(7,3), fig.ncol=1, fig.align = "center", out.width="80%", fig.cap="Minimal example; note the misalignment of (c) on compilation to pdf", fig.subcap=c('First', 'Second', 'Third')}
plot(1:10)
plot(cars, pch = 19)
boxplot(Sepal.Width ~ Species, data = iris)
```

---

Session info:

xfun::session_info('rmarkdown')
R version 4.3.1 (2023-06-16 ucrt)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 19045), RStudio 2023.6.1.524

Locale:
LC_COLLATE=English_United Kingdom.utf8 LC_CTYPE=English_United Kingdom.utf8
LC_MONETARY=English_United Kingdom.utf8 LC_NUMERIC=C
LC_TIME=English_United Kingdom.utf8

time zone: Europe/London
tzcode source: internal

Package version:
base64enc_0.1.3 bslib_0.5.1 cachem_1.0.8 cli_3.6.1
digest_0.6.33 ellipsis_0.3.2 evaluate_0.21 fastmap_1.1.1
fontawesome_0.5.2 fs_1.6.3 glue_1.6.2 graphics_4.3.1
grDevices_4.3.1 highr_0.10 htmltools_0.5.6 jquerylib_0.1.4
jsonlite_1.8.7 knitr_1.43 lifecycle_1.0.3 magrittr_2.0.3
memoise_2.0.1 methods_4.3.1 mime_0.12 R6_2.5.1
rappdirs_0.3.3 rlang_1.1.1 rmarkdown_2.24 sass_0.4.7
stats_4.3.1 stringi_1.7.12 stringr_1.5.0 tinytex_0.46
tools_4.3.1 utils_4.3.1 vctrs_0.6.3 xfun_0.40
yaml_2.3.7

Pandoc version: 3.1.1

---

• [YES ] installed and tested your bug with the development version of the rmarkdown package using remotes::install_github("rstudio/rmarkdown")?
  [Checked after initial session Info above]

[cderv]

Inspection of the LaTeX shows that this is due to a missing \newline after the final subfigure; inserting it manually in the LaTeX output corrects the alignment.

Can you share exactly where the new line should be inserted ? You can show the LaTeX code produced and what it should be for it work for this \begin{figure} block.

Thank you

[cderv]

I think I understand where you expect it to be...

It should be there:

\begin{figure}

{\centering \subfloat[First\label{fig:unnamed-chunk-1-1}]{\includegraphics[width=0.8\linewidth]{test_files/figure-latex/unnamed-chunk-1-1} }\newline\subfloat[Second\label{fig:unnamed-chunk-1-2}]{\includegraphics[width=0.8\linewidth]{test_files/figure-latex/unnamed-chunk-1-2} }\newline\subfloat[Third\label{fig:unnamed-chunk-1-3}]{\includegraphics[width=0.8\linewidth]{test_files/figure-latex/unnamed-chunk-1-3} }\newline

}

\caption{Minimal example; note the misalignment of (c) on compilation to pdf}\label{fig:unnamed-chunk-1}
\end{figure}

Those figures separators are introduced by knitr directly with its hook for plots in tex file. It will create a default fig.sep to put between the plots.

First, note that you can override the default using fig.sep chunk options. By adding a vector of the length of the plot (i.e fig.sep = rep("\\newline", 3), you'll get the result you want

---
output: 
  pdf_document:
    extra_dependencies: "subfig"
    keep_tex: true
    keep_md: true
---

```{r, fig.cap='Figure 1', fig.dim=c(7,3), fig.ncol=1, fig.align = "center", out.width="80%", fig.cap="Minimal example; note the misalignment of (c) on compilation to pdf", fig.subcap=c('First', 'Second', 'Third'), fig.sep = rep("\\newline", 3)}
plot(1:10)
plot(cars, pch = 19)
boxplot(Sepal.Width ~ Species, data = iris)
```

Our current default in knitr is to add \\newline by default except for last one
https://github.com/cderv/knitr/blob/7bc8b393e261c88f299bccc7eee40b4e952ebd57/R/hooks-latex.R#L78-L84

  fig.num = options$fig.num %n% 1L
  animate = options$fig.show == 'animate'
  fig.ncol = options$fig.ncol %n% fig.num
  if (is.null(fig.sep <- options$fig.sep)) {
    fig.sep = character(fig.num)
    if (fig.ncol < fig.num) fig.sep[seq(fig.ncol, fig.num - 1L, fig.ncol)] = '\\newline'
  }

I think we do that for fig.ncol to work as it should. Try more figures and fig.ncol more than 1 and it seems to work, without this last \newline

@yihui do you remember why seq(fig.ncol, fig.num - 1L, fig.ncol) ?
Should we consider a specific edge case of fig.ncol = 1 to have a new.line ?

I'll let you move to knitr if we consider more than providing fig.sep explicitly.

[yihui]

do you remember why seq(fig.ncol, fig.num - 1L, fig.ncol) ?

I don't remember. Perhaps I thought it was unnecessary to add \newline after the last figure since there's nothing after it.

Should we consider a specific edge case of fig.ncol = 1 to have a new.line ?

The special case is not only for fig.ncol = 1, but when fig.num is a multiple of fig.ncol. I just pushed a fix. @slrellison You can either follow @cderv's suggestion above (to specify fig.sep manually), or install the development version of knitr via

remotes::install_github('yihui/knitr')

[cderv]

Thank you !

[slrellison]

Thank you all! This is why I like Open Source !

[github-actions]

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