Does LaTeX have an array data structure?

arrays latex tex hbox
Rasto picture Rasto · Apr 15, 2010 · Viewed 14.1k times · Source

Are there arrays in LaTeX? I don't mean the way to typeset arrays. I mean arrays as the data structure in LaTeX/TeX as a "programming language". I need to store a number of vbox-es or hbox-es in an array. It may be something like "an array of macros".

More details: I have an environment that should typeset songs. I need to store some songs' paragraphs given as arguments to my macro \songparagraph (so I will not typeset them, just store those paragraphs). As I don't know how many paragraphs can be in one particular song I need an array for this. When the environment is closed, all the paragraphs will be typeset - but they will be first measured and the best placement for each paragraph will be computed (for example, some paragraphs can be put one aside the other in two columns to make the song look more compact and save some space).

Any ideas would be welcome. Please, if you know about arrays in LaTeX, post a link to some basic documentation, tutorial or just state basic commands.

Answer

topskip picture topskip · Apr 15, 2010

This is an array how it could be implemented in LaTeX:

\documentclass{article}
\begin{document}

\newcounter{mycounter}
\setcounter{mycounter}{1}

% ary is any prefix you want, it should not exist as a command.

\expandafter\newcommand\csname ary\the\value{mycounter} \endcsname{myfirstelement}
\stepcounter{mycounter}
\expandafter\newcommand\csname ary\the\value{mycounter} \endcsname{mysecondelement}

\csname ary1 \endcsname

or

\newcounter{index}
\setcounter{index}{2}

\csname ary\the\value{index} \endcsname

\end{document}

Run this through LaTeX (latex mydoc.tex or pdflatex mydoc.tex) and you see the output.

A short explanation: this creates two commands (with newcommand): ary1 and ary2. The \expandafter is needed because newcommand should not define \csname but the command created by \csname ... \endcsname. \expandafterjumps over the next token, in this case the control sequence \newcommand and executes the next command before TeX sees the \newcommand. That means, the first thing in the newcommand-lines TeX sees is the \csname...\endcsname construct, TeX executes it and then executes \newcommand with the result of the \csname...\endcsname construct. \csname foo\endcsname is the same as \foo, but you can use any character or even spaces in the command created by \csname...\endcsname.

This is not trivial. See the great book "TeX by topic" from Victor Eijkhout: http://eijkhout.net/texbytopic/texbytopic.html

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