How to use variables inside a command when generating a table?

Question

I'm not sure about the question, since I do not really understand why it fails.

I tend to use commands to generate my tables, and when I use the #1 style of accessing the arguments it works. But now I have a wider dataset, and need to use this trick: How to define a command that takes more than 9 arguments to get all the arguments together in one command.

Minimal example:

\documentclass[]{article}
\begin{document}

\newcommand\rowdata[2]{%
    \def\firstPoint{#1}%
    \def\secondPoint{#2}%
    \createRow
    % #1 & #2 \\ would work.
}
\newcommand\createRow{ %
    \wlog{\firstPoint \secondPoint} % it appears in the log 
    \firstPoint & \secondPoint \\ % this fails
}

\begin{table}
    \begin{tabular}{l l}
        \rowdata{a}{b}
        \rowdata{d}{b}
        \rowdata{a}{c}
    \end{tabular}
\end{table}
\end{document}

And this gives the following error:

! Undefined control sequence.
\createRow ...dPoint } \firstPoint & \secondPoint 
                                                  \\ 
l.16        \rowdata{a}{b}

If I remove the & it does work, but then I cannot create a table anymore.

So what is happening here?

Answer 1

In comments, the reason is pointed out: & besides other things ends and begins a group so the definition of \secondPoint is forgotten. Solution: use \gdef :

\documentclass[]{article}
\begin{document}

\newcommand\rowdata[2]{%
    \gdef\firstPoint{#1}%
    \gdef\secondPoint{#2}%
    \createRow
    % #1 & #2 \\ would work.
}
\newcommand\createRow{ %
    \wlog{\firstPoint \secondPoint} % it appears in the log 
    \firstPoint & \secondPoint \\ % this fails
}

\begin{table}
    \begin{tabular}{l l}
        \rowdata{a}{b}
        \rowdata{d}{b}
        \rowdata{a}{c}
    \end{tabular}
\end{table}
\end{document}

Answer 2

The stringstrings package has a \getargs command that works like Unix. It will parse a single argument into \argi, \argii, etc. The total number of arguments is in \narg.

\documentclass{article}
\usepackage{stringstrings}
\begin{document}
\getargs{1 2 3 4 5 6 7 8 9 10 11 12 FinalArgument}
There are \narg~arguments.  The thirteenth is \argxiii
\end{document}

The result to this example is:

There are 13 arguments. The thirteenth is FinalArgument

======

In answer to a request for a MWE, I note that stringstrings did suffer the same problem the user noticed above, which is that the getargs results were not global. However, I remedy that here with a \makeatletter redefinition of \getargs.

Then I redefined \rowdata to take one big space-separated argument. So here is how one prints a 12 column table with a command that generates the rows. Furthermore, the argument is merely space-separated data, not separate {} blocks.

AFTERTHOUGHT: The \rowdata command can take more than just typed data as its content. For example, you could have \today as part of the data, and it would take up three arguments (i.e., columns) of the table

Here is the code

\documentclass[]{article}
\usepackage{stringstrings}
\makeatletter
\renewcommand\getargs[2][q]{\+%
  \if v#1\def\@mode{q}\else\def\@mode{#1}\fi
  \edef\@argv{#2}%
  \@getstringlength{\@argv}{@stringsize}%
  \setcounter{@iargc}{0}%
  \whiledo{\value{@stringsize} > 0}{%
    \addtocounter{@iargc}{1}%
    \getaword[\@mode]{\@argv}{1}%
    \expandafter\global\expandafter\edef\csname arg\roman{@iargc}\endcsname{\thestring}%
    \removeword[e]{\@argv}%
    \edef\@argv{\thestring}%
    \@getstringlength{\@argv}{@stringsize}%
  }
  \edef\narg{\arabic{@iargc}}%
\?}
\makeatother
\newcommand\rowdata[1]{%
  \getargs{#1}
  \argi & \argii & \argiii & \argiv & \argv & \argvi & \argvii & 
  \argviii & \argix & \argx & \argxi & \argxii \\    }
\begin{document}
\begin{table}
    \begin{tabular}{l l l l l l l l l l l l}
        \rowdata{a b 3 4 5 6 7 8 9 10 11 12}
        \rowdata{d b blah 3 45 89 s rt 343 \today}
        \rowdata{a c 45 dfgf 454 454 fd 7 sds ssd s s}
    \end{tabular}
\end{table}
\end{document}