Align group_tt columns with multicolumn for tabular theme

[jsr-p]

This PR sets the columns created by group_tt into a multicolumn environment
to center the names above the columns that they span. This is done by
tabularray by default but not when using tabular.

The resulting table after the fix is the last table here:

Together with #378 the resulting table is:

Code:

df <- data.frame(
  has_bun = c(1, 1, 0, 0),
  has_cheese = c(1, 0, 1, 0),
  no_bun = c(0, 1, 1, 1),
  no_cheese = c(0, 1, 0, 1),
  full_meal = c(1, 0, 1, 1),
  veggie_compatible = c(1, 0, 1, 1)
)


df |>
  tt() |>
  setNames(c(
    "Bun",
    "Cheese",
    "No Bun",
    "No Cheese",
    "Meal",
    "Veggie"
  )) |>
  style_tt(
    align = "cccccc"
  ) |>
  theme_tt("tabular") |>
  group_tt(
    j = list("Burger Components" = 1:2, "Omission" = 3:4, "Meal Options" = 5:6)
  ) |>
  group_tt(
    j = list("Overall" = 1:6)
  ) |>
  save_tt("burger_table.tex", overwrite = TRUE)

latex code:

\begin{tabular}{llllll}
\hline
\multicolumn{6}{c}{Overall} \\ \cmidrule(lr){1-6}
\multicolumn{2}{c}{Burger Components} & \multicolumn{2}{c}{Omission} & \multicolumn{2}{c}{Meal Options} \\ \cmidrule(lr){1-2}\cmidrule(lr){3-4}\cmidrule(lr){5-6}
Bun & Cheese & No Bun & No Cheese & Meal & Veggie \\ \hline
1 & 1 & 0 & 0 & 1 & 1 \\
1 & 0 & 1 & 1 & 0 & 0 \\
0 & 1 & 1 & 0 & 1 & 1 \\
0 & 0 & 1 & 1 & 1 & 1 \\
\hline
\end{tabular}

[vincentarelbundock]

Thanks for this!

One problem is that currently, this will change all LaTeX tables. This is undesirable, because we normally want to use the colspan feature of tabularray, which is much "cleaner" than modifying individual cells.

My guess is that there has to be a conditional check to make sure we are in tabular theme, like here: https://github.com/vincentarelbundock/tinytable/pull/379/files#diff-22fb54c6e87c73db96b6bf05312fa0c45d0f6580669a1e88435c4e38348f15eaR22

Currently, this check is a bit hard to do, because theme_tabular() does not actually modify the table@theme string. Frankly, I don't remember why I left default there. It might be fine to change the theme, but this should be tested. See https://github.com/vincentarelbundock/tinytable/blob/main/R/theme_tabular.R#L7

Finally, I would really, really like a change like this to be in the finalize function of the theme_tabular.R file. If we can be clever and find a way to put that code in there, it would be awesome. Modifying group_tabularray(), which is generic code for all themes, should only be a last recourse.

[jsr-p]

Thanks a lot for the feedback 😄
I will need to think about how best to adjust my PR to address the points you mentioned

[vincentarelbundock]

Closing this PR to keep the repository clean, and because it would require a major rewrite, as describe above.

Also, if someone wants to implement another version of this, I think we should first have a discussion about goals and scope. I recognize that the tabular environment is nice because it is a lightweight and basic LaTeX environment, but there are good reasons why I chose tabularray. It really keeps the code clean and simple. One of the design principles is to not modify the content of cells or wrap text in \multicolumn{} or \emph{}, using the tabularray styling commands instead.

I feel it is a bit of a slippery slope to re-implement styling and structural features "by hand".

Moreover, it is possible to have multiple "minimal" tabularray environments, with multicolumn, and to include them side-by-side in a single environment:

https://tex.stackexchange.com/questions/671696/how-to-position-two-tabularray-tables-side-by-side-in-such-a-way-that-their-top