How can I store variables in lists and make use of them?

Question

This question is clearly related to How can I store variables and iterate over them?.

I'm sorry to ask such a close one, but I really don't understand the answer in plain TeX by David Carlisle.

Basically, I'd like to make a template in LaTeX, compatible with plain LaTeX/pdfLaTeX (no lua code), with as few dependencies as possible, that would allow me to get personal information this way:

\adduser{John Doe}{UK}
\adduser{M. Dupont}{France}
\adduser{M. Martin}{Belgium}{France}
\adduser{Jan Jansen}{Netherlands}
\adduser{Matti Meikäläinen}{Netherlands}{Finland}

And output something like that:

John Doe(a), M.Dupont(b), M. Martin(b, c), Jan Jansen(d), Matti Meikäläinen(d, e)

a: UK

b: France

c: Belgium

d: Netherlands

e: Finland

I'm sure this is possible, but in plain LaTeX, this seems very difficult. Any idea?

Answer 1

Although there are some similarities with the other question, there are enough differences in the specifics that the code looks rather different. I added some comments this time:-)

\documentclass{article}

% 8bit encoded letters
\usepackage[latin1]{inputenc}

% a counter for locations
\newcounter{places}
\renewcommand\theplaces{\alph{places}}

% use @ in code
\makeatletter
% initialise the lists
\def\usernames{}
\def\userplaces{}


% #1 is person #2 is comma separated list
% It is harder and against LaTeX syntax rules
% to do as suggested and to have a variable number of
% brace groups.
\def\adduser#1#2{%
% add a comma if not the first
\ifx\usernames\@empty\else\g@addto@macro\usernames{, }\fi
%
% add the name and the start of the list of letters
% \@gobble will eat a comma before the first
\g@addto@macro\usernames{#1 (\@gobble}
%
% loop through a comma separated list
\@for\@tmp:=#2\do{%
% If we haven't seen this country before
% increment the counter
% Add the counter and the place name to the userplaces list
\expandafter\ifx\csname place@\@tmp\endcsname\relax
  \stepcounter{places}%
  \protected@edef\userplaces{\userplaces\par\theplaces: \@tmp}%
  \expandafter\edef\csname place@\@tmp\endcsname{\theplaces}%
\fi
% now get the letter stored for this place and add it to the list
\edef\@tmpb{\noexpand\g@addto@macro\noexpand\usernames{,\csname place@\@tmp\endcsname}}%
\@tmpb}
% add the closing )
\g@addto@macro\usernames{)}%
}
\makeatother


\adduser{John Doe}{UK}
\adduser{M. Dupont}{France}
\adduser{M. Martin}{Belgium,France}
\adduser{Jan Jansen}{Netherlands}
\adduser{Matti Meikäläinen}{Netherlands,Finland}

\begin{document}

\usernames

\userplaces

\end{document}

Answer 2

The following solution allows you to submit more than one user name when calling \adduser. It will also sort the user names and place indices.

\documentclass[12pt]{article}
\usepackage{catoptions}
\makeatletter
\newcounter{placecnt}
\def\printplaces{}
\def\printusers{\noindent\userlist\def\userlist{}}
\def\auxuserlist{}
\def\cptxappto#1#2{\protected@edef#1{#1#2}}
\def\cptalphasortcommalist#1#2{%
  \begingroup
  \def\sort@tempa{}%
  \cptdocommalist*#1{%
    \cptxappto\sort@tempa{{\unexpanded{##1}}}%
  }%
  \cptalphasort\sort@tempa#2%
  \def#1{}%
  \cptdosisolist*\sort@tempa{%
    \cptxappto#1{\ifx#1\@empty\else,\fi\unexpanded{##1}}%
  }%
  \postgroupdef#1\endgroup
}

\begingroup
\catcode`\~=13
% #1= comma separated list of persons.
% #2= comma separated list of affiliations/places.
\gdef\adduser#1#2{%
  \def\userlist{}%
  \let\sav@nobreakspace~%
  \let~\relax
  \cptdocommalist{#1}{%
    \ifcsname thisuserplaces@\detokenize{##1}\endcsname\else
      \csn@edef{thisuserplaces@\detokenize{##1}}{}%
      \cptxappto\auxuserlist{\ifx\auxuserlist\@empty\else,\fi##1}%
    \fi
    \cptdocommalist{#2}{%
      \ifcsname thisplaceid@\detokenize{####1}\endcsname\else
        \stepcounter{placecnt}%
        \cptxappto\printplaces{%
          \endgraf\noindent
          \textsuperscript{\alph{placecnt}}\unskip####1%
        }%
        \csn@edef{thisplaceid@\detokenize{####1}}{\alph{placecnt}}%
      \fi
      \edef\am@tempa{\@nameuse{thisplaceid@\detokenize{####1}}}%
      \edef\am@tempb{\@nameuse{thisuserplaces@\detokenize{##1}}}%
      \xifinsetTF{,\am@tempa,}{,\am@tempb,}{}{%
        \aftercsname\cptxappto{thisuserplaces@\detokenize{##1}}{%
          \ifx\am@tempb\@empty\else,\fi\am@tempa
        }%
      }%
    }%
  }%
  \cptalphasortcommalist\auxuserlist<%
  \cptdocommalist*\auxuserlist{%
    \edef\am@tempa{\@nameuse{thisuserplaces@\detokenize{##1}}}%
    \cptalphasortcommalist\am@tempa<%
    \cptxappto\userlist{%
      \ifx\userlist\@empty\else, \fi
      ##1\unskip\textsuperscript{\am@tempa}%
    }%
  }%
  \let~\sav@nobreakspace
  \undefcs\sav@nobreakspace
}
\endgroup
\makeatother

% Note repeated entry of M. Martin for the same and different locations:
\adduser{M.~Martin, John Doe}{UK, Germany}
\adduser{M.~Martin, D.D.D.~Damiaan}{Belgium}
\adduser{M.~Martin, N.~Johnson}{Belgium, France}
\adduser{M.~Dupont}{France}
\adduser{John Doe, Jan Jansen}{Netherlands, UK}
\adduser{Matti Meikäläinen, M.~Dupont}{Netherlands, Finland}
\adduser{Steve Binns}{UK}

\begin{document}
\printusers
\par\bigskip
\printplaces
\end{document}