To create a diagonal line inside a merged cell

[Yarakashi-Kikohshi]

I'm trying to draw only diagonal lines using \diagbox.

When drawing a diagonal line between merged cells, it is not possible to draw a diagonal line from the upper left corner to the lower right corner as shown below. I know that \diagbox can be adjusted by imposing multiple options, but I couldn't figure out how to get the desired result.

I created the following as a simple example.

\documentclass[ border = 3pt ]{standalone}
\usepackage{tabularray}
\UseTblrLibrary{diagbox}
\newcommand{\onlySlash}{
  \diagbox[
    height = 2\line+\abovesep+\belowsep,
  ]{}{}%
}
\begin{document}

\begin{tblr}{
    hlines, vlines,
    columns = {
      halign = c, valign = m,
      % co = 1,
    },
    cell{2}{2} = { r = 2, c = 1 }{},
  }
  single cell & single cell \\
  merged cell & \onlySlash  \\
  merged cell & \onlySlash  \\
\end{tblr}

\end{document}

I am expecting an option specification that satisfies the following requirements.

• Column width depends on contents of cells other than \diagbox
• Don't specify a specific value
• Even relative column widths like co = 1 are automatically adjusted

Edit

I found that height requires two lines of abovesep and belowsep specifications. Therefore, modify it as follows.

- height = 2\line+\abovesep+\belowsep,
+ height = 2\line+2\abovesep+2\belowsep,

When I look at some site pages, I see a statement saying that width should be \linewidth. However, if you actually specify width = \linewidth, the column width will increase.

code

\documentclass[ border = 3pt ]{standalone}
\usepackage{tabularray}
\UseTblrLibrary{diagbox}
\newcommand{\onlySlash}{
  \diagbox[
    height = 2\line+2\abovesep+2\belowsep,
    %
    % Add this ↓
    width = \linewidth
  ]{}{}%
}
\begin{document}

\begin{tblr}{
    hlines, vlines,
    columns = {
      halign = c, valign = m,
      % co = 1,
    },
    cell{2}{2} = { r = 2, c = 1 }{},
  }
  single cell & single cell \\
  merged cell & \onlySlash  \\
  merged cell & \onlySlash  \\
\end{tblr}

\end{document}

---

In addition, if you check the column width of 2nd column on the PDF without \diagbox, you can see that it is 55pt, so I actually specified width = 55pt. (I didn't expect this kind of specification method, but I tried to see if it was possible.)

code

\documentclass[ border = 3pt ]{standalone}
\usepackage{tabularray}
\UseTblrLibrary{diagbox}
\newcommand{\onlySlash}{
  \diagbox[
    height = 2\line+2\abovesep+2\belowsep,
    %
    % Add this ↓
    width = 55pt
  ]{}{}%
}
\begin{document}

\begin{tblr}{
    hlines, vlines,
    columns = {
      halign = c, valign = m,
      % co = 1,
    },
    cell{2}{2} = { r = 2, c = 1 }{},
  }
  single cell & single cell \\
  merged cell & \onlySlash  \\
  merged cell & \onlySlash  \\
\end{tblr}

\end{document}

---

Also, considering the values of leftsep/rightsep, I also tried specifying the following:

code

\documentclass[ border = 3pt ]{standalone}
\usepackage{tabularray}
\UseTblrLibrary{diagbox}
\newcommand{\onlySlash}{
  \diagbox[
    height = 2\line+2\abovesep+2\belowsep,
    %
    % Add this ↓
    width = 43pt+\leftsep+\rightsep
  ]{}{}%
}
\begin{document}

\begin{tblr}{
    hlines, vlines,
    columns = {
      halign = c, valign = m,
      % co = 1,
    },
    cell{2}{2} = { r = 2, c = 1 }{},
  }
  single cell & single cell \\
  merged cell & \onlySlash  \\
  merged cell & \onlySlash  \\
\end{tblr}

\end{document}

[muzimuzhi]

See a general-purpose attempt I just posted in #387 (comment).

[Yarakashi-Kikohshi]

@muzimuzhi, thank you.

It is a very developmental workaround, almost a black box for me as I am unfamiliar with Expl3, but it works as expected 😄