Problem with \pgfmathparse and font style of array elements

Question

There are probably other ways to do that, but I was happy I've found this code working just fine for my needs:

\documentclass{article}
\usepackage{tikz}
\newcounter{grpcnt}
\def\groups{grp1, grp2, grp3}
\def\keyvals{{ {"key 00/val 00, key 01/val 01"}, {"key 10/val 10, key 11/val 11, key 12/val 12"}, {"key 20/val 20"} }}
\begin{document}
\setcounter{grpcnt}{0}
\foreach \grp in \groups {
    \section*{\grp}
    \pgfmathparse{\keyvals[\thegrpcnt]}
    \foreach \key/\val in \pgfmathresult
    {
        \textbf{\key}: \val \\[1ex]
    }
    \addtocounter{grpcnt}{1}
}
\end{document}

The problem I have is if I try to store any font styling in the 2nd array, say an \emph{} on the first value 00:

\documentclass{article}
\usepackage{tikz}
\newcounter{grpcnt}
\def\groups{grp1, grp2, grp3}
\def\keyvals{{ {"key 00/val \emph{00}, key 01/val 01"}, {"key 10/val 10, key 11/val 11, key 12/val 12"}, {"key 20/val 20"} }}
\begin{document}
\setcounter{grpcnt}{0}
\foreach \grp in \groups {
    \section*{\grp}
    \pgfmathparse{\keyvals[\thegrpcnt]}
    \foreach \key/\val in \pgfmathresult
    {
        \textbf{\key}: \val \\[1ex]
    }
    \addtocounter{grpcnt}{1}
}
\end{document}

Which will break compilation. I found out that some other types of commands are seen and interpreted correctly (e.g., some special characters like \AE work just fine), but any font syling command I've tried (\large, \textbf{}, \itshape, etc.) have failed. Any idea why and/or how I could store some font styling in the 2nd array? Thanks! :)

Answer 1

The problem is that \pgfmathparse performs \edef and commands such as \emph don't survive it.

You get what you need by preceding such commands with \noexpand:

\documentclass{article}
\usepackage{tikz}
\newcounter{grpcnt}
\def\groups{grp1, grp2, grp3}
\def\keyvals{{ {"key 00/val \noexpand\emph{00}, key 01/val 01"},
  {"key 10/val 10, key 11/val 11, key 12/val 12"}, {"key 20/val 20"} }}
\begin{document}

\setcounter{grpcnt}{0}

\foreach \grp in \groups {%
    \section*{\grp}
    \pgfmathparse{\keyvals[\thegrpcnt]}
    \foreach \key/\val in \pgfmathresult
    {%
      \textbf{\key}: \val \\[1ex]
    }%
    \addtocounter{grpcnt}{1}%
}

\end{document}

What are the “dangerous” commands? It's not easy to tell. But font changing commands surely are, as well as some other text producing ones.

---

A completely different implementation that doesn't require any protection; the input of groups is changed, but I believe that a group and its corresponding list should be input together.

\documentclass{article}
\usepackage{xparse,indentfirst}

\ExplSyntaxOn
\NewDocumentCommand{\definegroup}{mm}
 {
  \shrodi_define_group:nn { #1 } { #2 }
 }
\NewDocumentCommand{\processgroups}{ }
 {
  \shrodi_process_groups:
 }

\seq_new:N \g_shrodi_groups_seq
\cs_new:Npn \__shrodi_make_name:n #1
 {
  g_shrodi_\tl_to_str:n{#1}_clist
 }
\cs_new_protected:Npn \shrodi_define_group:nn #1 #2
 {
  \seq_gput_right:Nn \g_shrodi_groups_seq { #1 }
  \clist_new:c { \__shrodi_make_name:n { #1 } }
  \clist_gset:cn { \__shrodi_make_name:n { #1 } } { #2 }
 }
\cs_new_protected:Npn \shrodi_process_groups:
 {
  \seq_map_inline:Nn \g_shrodi_groups_seq
   {
    \section* { ##1 }
    \clist_map_inline:cn { \__shrodi_make_name:n { ##1 } }
     {
      \shrodi_print_contents:nn ####1
     }
   }
 }
\cs_new_protected:Npn \shrodi_print_contents:nn #1 #2
 {
  \textbf{ #1 }: ~ #2 \par \medskip
 }
\ExplSyntaxOff

\definegroup{grp1}{
  {key 00}{val \emph{00}},
  {key 01}{val 01}
}
\definegroup{grp2}{
  {key 10}{val 10},
  {key 11}{val 11},
  {key 12}{val 12}
}
\definegroup{grp3}{
  {key 20}{val 20}
}

\begin{document}

\processgroups

\end{document}

Answer 2

Option 1

You could store the information indirectly. For example, along with the key and value, you could add a third element to signal a format directive. Your code would then test that and format the value of e.g. \val appropriately.

Note that the following example works by adding the text formatting command without the leading backslash e.g. emph not \emph. The command is then reconstructed using \csname ... \endcsname. Note that I have no idea if this is a good idea or not.

\documentclass{article}
\usepackage{tikz}
\newcounter{grpcnt}
\def\groups{grp1, grp2, grp3}
\def\keyvals{{ {"key 00/val 00/emph, key 01/val 01"}, {"key 10/val 10, key 11/val 11, key 12/val 12"}, {"key 20/val 20"} }}
\begin{document}
\setcounter{grpcnt}{0}
\foreach \grp in \groups {
    \section*{\grp}
    \pgfmathparse{\keyvals[\thegrpcnt]}
    \foreach \key/\val/\form in \pgfmathresult
    {
      \edef\tempa{}%
      \edef\tempb{\form}%
        \textbf{\key}: \ifx\tempa\tempb\val\else\expandafter\csname\form\endcsname{\val}\fi \\[1ex]
    }
    \addtocounter{grpcnt}{1}
}
\end{document}

Option 2

Just use the method mentioned in the documentation for pgf and protect the commands with \noepand. (See e.g. page 529 of the manual.)

\documentclass{article}
\usepackage{tikz}
\newcounter{grpcnt}
\def\groups{grp1, grp2, grp3}
\def\keyvals{{ {"key 00/val \noexpand\emph{00}, key 01/val 01"}, {"key 10/val 10, key 11/val 11, key 12/val 12"}, {"key 20/val 20"} }}
\begin{document}
\setcounter{grpcnt}{0}
\foreach \grp in \groups {
    \section*{\grp}
    \pgfmathparse{\keyvals[\thegrpcnt]}
    \foreach \key/\val in \pgfmathresult
    {
        \textbf{\key}: \val \\[1ex]
    }
    \addtocounter{grpcnt}{1}
}
\end{document}