Refine Latex Tables with Group Cols

[kbrevoort]

Summary

I was making some tables for a paper I'm writing this afternoon and found a few minor issues when Latex tables are created with row_group_as_column = TRUE that this PR addresses. There are three changes:

1. The multirow Latex command used for the group column use an "=" which instructs Latex to respect the column widths that have been selected. However, when no column widths have been selected, it defaults to using all the width available. This PR changes this behavior, replacing the "=" with "*", so the natural width of the column will be used.
2. There was a bug in the code that caused an error when assigning widths to the group column that I've fixed. (There was a boolean vector where I wanted to count the TRUE values, but instead was taking the length of the vector.)
3. Stubhead labels were not being properly centered when widths were specified. The stubhead label is now properly centered.

This Quarto code:

---
title: "Untitled"
execute: 
  echo: false
format: pdf
---

```{r}
#| include: false
library(tidyverse)
library(gt)

tbl <- select(exibble, group, row, num, currency) |>
  gt(rowname_col = 'row', 
     groupname_col = 'group',
     row_group_as_column = TRUE) |>
  tab_row_group(label = 'Group 1', 
                rows = 1:3) |>
  tab_stubhead('Stubhead') |>
  tab_options(latex.use_longtable = TRUE)

tbl

currently produces this output:

With this PR, the same code will now produce:

Related GitHub Issues and PRs

None.

Checklist

• [x ] I understand and agree to the Code of Conduct.
• [x ] I have listed any major changes in the NEWS.
• [x ] I have added testthat unit tests to tests/testthat for any new functionality.

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[olivroy]

Thanks for your diligence! Please add news for the change!

I think that this fixes #1799.

[olivroy]

@kbrevoort Could you run source("scripts/visual-test-latex.R") and commit the result?

[olivroy]

@kbrevoort Wow! It actually fixes #1799. See the second table in the visual examples. The second page of https://github.com/rstudio/gt/blob/8744851023d7bee722d74bfd9693b17cb3b232e2/pkgdown/assets/gt-latex.pdf no longer is baffled

Before the PR:

This PR:

[rich-iannone]

Thank you @kbrevoort and @olivroy ! Will merge this in now.