Can citation numbers be stored as variables, then used in my tex file?

Question

I'm trying to create a "flow chart" of papers that shows the progression of key ideas over time. A very basic example is this:

\documentclass{article}
\usepackage{tikz}


\begin{document}

\newcommand{\oldpaper}{2}
\newcommand{\newpaper}{1}

\begin{tikzpicture}[show/.style={circle,draw}]
\node[show]    (\newpaper)    at    (0,2)     [label=right:{This 2011 paper utilizes the good ideas and makes them even better}]    {\newpaper};
\node[show]    (\oldpaper)   at     (0,0)    [label=right:{This paper came out in 1900 and has good ideas}]    {\oldpaper};
\draw[->]    (\oldpaper) -- (\newpaper);
\end{tikzpicture}


\bibliographystyle{amsplain}
\begin{thebibliography}{10}

\bibitem{newpaper}C. Charles, \emph{New Stuff}, 2011.

\bibitem{oldpaper}H. Huckley, \emph{Old Stuff}, 1900.


\end{thebibliography}



\end{document}

The point is that the circular nodes have a number inside of them that equals the number in the bibliography, so if you're looking at the flowchart and see a paper that looks interesting, you can look at the references to see exactly what paper it is. The only way I could figure out how to do this somewhat efficiently was by the \newcommand stuff -- but this requires me compiling the code, looking at the bibliography, and then manually defining the \newpaper and \oldpaper to be what they "should" be. If I add another reference, say,

\documentclass{article}
\usepackage{tikz}


\begin{document}

\newcommand{\oldpaper}{2}
\newcommand{\newpaper}{1}

\begin{tikzpicture}[show/.style={circle,draw}]
\node[show]    (\newpaper)    at    (0,2)     [label=right:{This 2011 paper utilizes the good ideas and makes them even better}]    {\newpaper};
\node[show]    (\oldpaper)   at     (0,0)    [label=right:{This paper came out in 1900 and has good ideas}]    {\oldpaper};
\draw[->]    (\oldpaper) -- (\newpaper);
\end{tikzpicture}


\bibliographystyle{amsplain}
\begin{thebibliography}{10}

\bibitem{newerpaper}B. Becker, \emph{Even Newer Stuff}, 2012.

\bibitem{newpaper}C. Charles, \emph{New Stuff}, 2011.

\bibitem{oldpaper}H. Huckley, \emph{Old Stuff}, 1900.

\end{thebibliography}


\end{document} 

then I have to redefine my \oldpaper and \newpaper variables by hand. It's also important that the nodes are named with the same variable, that way the drawing looks right no matter what value the variables have. My real flow chart has over 30 papers in it, and the real bibliography has over 50. Obviously it's getting cumbersome to do this by hand, so I'm wondering if I can somehow use \cite{} and extract what the reference number "should be," and name/number the nodes accordingly, and it will update dynamically should I add or drop a reference (some of my references don't show up in the flow chart). I tried adding

\makeatletter
\renewcommand*{\@biblabel}[1]{#1}
\makeatother

in the preamble, then defining

\newcommand{\oldpaper}{\cite{oldpaper}}

so that the variable \oldpaper would have the value equal to the current citation number \cite{oldpaper} but that didn't work at all. The error message is:

Argument of \XC@definec@lor has an extra }

This is beyond my TeX knowledge, and I've spent hours reading about BiBTeX and googling to no avail. Does anyone know how to solve this? Thank you in advance, and I hope my question is clear.

Answer 1

Why do you want numbers as node names? You could simply use the bibkeys:

\documentclass{article}
\usepackage{tikz}

\begin{document}

\begin{tikzpicture}[show/.style={circle,draw}]
\node[show]    (newpaper)    at    (0,2)    
    [label=right:{This 2011 paper ...}]    
    {\cite{newpaper}};
\node[show]    (oldpaper)   at     (0,0)    
     [label=right:{This paper came out in 1900 ...}]    
    {\cite{oldpaper}};
\draw[->]    (oldpaper) -- (newpaper);
\end{tikzpicture}


\bibliographystyle{amsplain}
\begin{thebibliography}{10}
\bibitem{newerpaper}B. Becker, \emph{Even Newer Stuff}, 2012.
\bibitem{newpaper}C. Charles, \emph{New Stuff}, 2011.
\bibitem{oldpaper}H. Huckley, \emph{Old Stuff}, 1900.
\end{thebibliography}
\end{document} 

Answer 2

The reason that your method doesn't work is that LaTeX normally does some tests to make sure that you're citing something that has a corresponding \bibitem, and it also lets you cite more than one key in each \cite command, so \cite{key} isn't so simple that it can just expand to the citation number for key.

The citation numbers for citation key key are internally stored in a macro \b@key, and these are LaTeX internals ("protected" from normal access by the @ symbol). You can access them, but are advised not to. For example, what would you expect the behaviour to be if you're using a non-standard (but supported) extension to LaTeX's bibliography system? Can you be certain that using something like hyperref won't change the internals to accomplish its goals?

So Ulrike's suggestion that you should try to find another way to do what you want is good, but what if you want to change the citation style only for your tikz nodes, but not in the bibliography itself or in other references? In such case, you might like to use something like the \citekey macro I've defined below, which acts like a wrapper to obtaining the internal values for you. Note that it will require two runs to be correct, and there may be better ways of doing this...

\documentclass{article}
\usepackage{tikz}

%if we were to try to do \newcommand{\oldpaper}{\b@oldpaper}, we would need \makeatletter ... \makeatother protection around the \newcommand, but we're using \csname...\endcsname here, so we don't need to worry about that!
\newcommand*{\citekey}[1]{\csname b@#1\endcsname}

\begin{document}

%\newcommand{\oldpaper}{2}
%\newcommand{\newpaper}{1}
\newcommand{\oldpaper}{\citekey{oldpaper}}
\newcommand{\newpaper}{\citekey{newpaper}}


\begin{tikzpicture}[show/.style={circle,draw}]
\node[show]    (\newpaper)    at    (0,2)     [label=right:{This 2011 paper utilizes the good ideas and makes them even better}]    {\newpaper};
\node[show]    (\oldpaper)   at     (0,0)    [label=right:{This paper came out in 1900 and has good ideas}]    {\oldpaper};
\draw[->]    (\oldpaper) -- (\newpaper);
\end{tikzpicture}


\bibliographystyle{amsplain}
\begin{thebibliography}{10}

\bibitem{newerpaper}B. Becker, \emph{Even Newer Stuff}, 2012.

\bibitem{newpaper}C. Charles, \emph{New Stuff}, 2011.

\bibitem{oldpaper}H. Huckley, \emph{Old Stuff}, 1900.


\end{thebibliography}




\end{document}