(HTML) Indices are changed after cells are merged with rowspan

[J-Moravec]

This could perhaps be emphasized in documentation because it took me quite a bit to understand what is going on.

1. style_tt(rowspan = ...) to merge rows
2. style_tt(j = ... , i = which(...)) -- suddenly columns are styled (e.g., coloured) in weird ragged way.

Switching order of operations doesn't help (likely they are evaluating lazily in a particular order)

This makes conditional styling together with rowspan essentially impossible (without adding a bunch of dummy column).

[vincentarelbundock]

Interesting. I think this may be HTML-specific. In LaTeX, all entries stay in the table and we use a tabularray argument to stretch cells. Since all cells stay in place, we can still refer and style them using the same indices.

In HTML, I believe that we "drop" cells, so indexing probably changes. This may require us to store a new S4 slot with information about spans, so that we can adjust indices appropriately. That's an interesting problem I had not considered before.

Super busy at work these days, but I'll take a look when I find some time. Thanks for the report!

[J-Moravec]

MRE:

d = data.frame(1:2, 3:4)

# text output works well
tt(d) |> style_tt(j = 1, i = 1, rowspan = 2) |> style_tt(j = 1, color = "orange", italic = TRUE)

# +------+------+
# | X1.2 | X3.4 |
# +======+======+
# | *1*  | 3    |
# +------+------+
# | **   | 4    |
# +------+------+ 

# HTML output doesn't(t
tt(d) |> style_tt(j = 1, i = 1, rowspan = 2) |> style_tt(j = 1, color = "orange", italic = TRUE) |> save_tt("test.html")

We wanted to highlight first column. Instead, the first cell in a row is always highlighted, since the actual first cell was deleted by rowspan. For complex HTML tables. So to fix that, an empty dummy column needs to be inserted, or any conditional highlighting needs to compensate indexing for this,

[vincentarelbundock]

This PR is a proof of concept to handle the rowspan issue reported here.

#374

Problems:

1. Ugly
2. Does not handle colspan

Orange works despite rowspan. Blue does not work because of colspan

pkgload::load_all()
tt(head(iris)) |> 
    style_tt(j = 1, i = 1, rowspan = 2, colspan = 2) |> 
    style_tt(i = 1, color = "blue") |> 
    style_tt(j = 1, color = "orange", italic = TRUE)
    save_tt("example.html", overwrite = TRUE)