grid_tables with multicol/multirow too wide

[DavidNemeskey]

Explain the problem.

I am creating beamer presentations from pandoc markdown. I tried to add a table with multicol + multirow, using the grid_tables format (which is the only one that supports these features if I understand correctly). Unfortunately, the tables generated are way too wide. I used two of the examples from the documentation. In the first one (with multicol), the first column is way too wide, unnecessarily so. In the second (multicol + multirow), the table is so wide that it hangs off the slide on the right, even though all the content fits comfortably on the page.

pandoc -t beamer -o output.pdf --slide-level 2 pandoc_table.md

The MWE is here: pandoc_table.md.

This is how it looks like:

Pandoc version?

Pandoc: 3.1.8
OS: KDE Neon (6.2.0-34-generic #34~22.04.1-Ubuntu x86_64)
Texlive: 2021.202204-1

[chagmed]

Alas, grid_tables makes me feel utterly defeated. I can code in several languages, am very comfortable with many complex tech stacks, but I cannot for the life of me figure out how to write well-behaved grid tables consistently and predictably. Not good when examples from the docs don't work.

[jgm]

Yes, definitely problematic, we'll look into it.
I note that even with -t latex we get an over-wide table.

Here's the tex produced for the first table:

\begin{longtable}[]{@{}
  >{\raggedright\arraybackslash}p{(\columnwidth - 4\tabcolsep) * \real{0.1944}}
  >{\raggedright\arraybackslash}p{(\columnwidth - 4\tabcolsep) * \real{0.1111}}
  >{\raggedright\arraybackslash}p{(\columnwidth - 4\tabcolsep) * \real{0.1528}}@{}}
\toprule\noalign{}
\multicolumn{2}{@{}l}{%
\begin{minipage}[b]{\linewidth}\raggedright
Property
\end{minipage}} & \begin{minipage}[b]{\linewidth}\raggedright
Earth
\end{minipage} \\
\midrule\noalign{}
\endhead
\multirow{3}{*}{Temperature 1961-1990} & min & -89.2 °C \\
& mean & 14 °C \\
& min & 56.7 °C \\
\bottomrule\noalign{}
\end{longtable}

[jgm]

Output with -t latex:

Here the width is okay on the first table but there is overlap; the second table is too wide.

[jgm]

I think we need to pass a parameter for cell width to \multicolumn; looks like it's taking the whole table width.

[jgm]

With these tables we get proper widths. The change is that a real width is computed for each \multicolumn, based on the columns containing it.

\begin{longtable}[]{@{}
  >{\raggedright\arraybackslash}p{(\columnwidth - 4\tabcolsep) * \real{0.1944}}
  >{\raggedright\arraybackslash}p{(\columnwidth - 4\tabcolsep) * \real{0.1111}}
  >{\raggedright\arraybackslash}p{(\columnwidth - 4\tabcolsep) * \real{0.1528}}@{}}
\toprule\noalign{}
\multicolumn{2}{@{}p{(\columnwidth - 4\tabcolsep) * \real{0.21}}}{%
\begin{minipage}[b]{\linewidth}\raggedright
Property
\end{minipage}} & \begin{minipage}[b]{\linewidth}\raggedright
Earth
\end{minipage} \\
\midrule\noalign{}
\endhead
\bottomrule\noalign{}
\endlastfoot
\multirow{3}{*}{Temperature 1961-1990} & min & -89.2 °C \\
& mean & 14 °C \\
& min & 56.7 °C \\
\end{longtable}


\begin{longtable}[]{@{}
  >{\raggedright\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.3056}}
  >{\raggedright\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.1111}}
  >{\raggedright\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.1111}}
  >{\raggedright\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.1111}}@{}}
\toprule\noalign{}
\multirow{2}{*}{\begin{minipage}[b]{\linewidth}\raggedright
Location
\end{minipage}} & \multicolumn{3}{p{(\columnwidth - 6\tabcolsep) * \real{0.5278}}@{}}{%
\begin{minipage}[b]{\linewidth}\raggedright
Temperature 1961-1990 in degree Celsius
\end{minipage}} \\
& \begin{minipage}[b]{\linewidth}\raggedright
min
\end{minipage} & \begin{minipage}[b]{\linewidth}\raggedright
mean
\end{minipage} & \begin{minipage}[b]{\linewidth}\raggedright
max
\end{minipage} \\
\midrule\noalign{}
\endhead
\bottomrule\noalign{}
\endlastfoot
Antarctica & -89.2 & N/A & 19.8 \\
Earth & -89.2 & 14 & 56.7 \\
\end{longtable}

In the first case there is still overlap, but that could at least be fixed by making the cell bigger in the source.

[jgm]

to fix the remaining (overlap) issue, we need to add an explicit width to the \multirow (instead of * = "use natural width").