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Suppose I want a \gotocolumn command, with the following behavior: in a tabular with n or more columns, \gotocolumn{n} would expand to the shortest combination of \\ and & necessary to bring us forward into the n'th column. So for instance...

  • In the first column of a table, \gotocolumn{3} would expand to & &.
  • In the second column of a table, \gotocolumn{3} would expand to &.
  • In the third column of a table, \gotocolumn{3} would expand to \relax.
  • In the fourth or subsequent column of a table, \gotocolumn{3} would expand to \\ & &.

Has this been done? Could it be done? Thoughts on how?

Leah Velleman
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1 Answers1

2

You can do some bookkeeping when new columns and rows are started. If you really want to you can redefine & and \\ I chose to introduce some new macros that just "call" the normal ones and do some additional work. It looks like this:

\documentclass{article}
\newcounter{currCol}
\setcounter{currCol}{1}
\def\amp{\stepcounter{currCol}&}
\def\nl{\\\setcounter{currCol}{1}}
\newcounter{numCols}
\setcounter{numCols}{3}
\def\gotocolumn#1{%
  \ifnum\the\value{currCol}=#1%done
  \else%
    \ifnum\the\value{currCol}<#1% before same row
      \amp\gotocolumn{#1}%
    \else% after, next row
      \ifnum\the\value{currCol}<\the\value{numCols}% need additional columns
        \amp\gotocolumn{#1}%
      \else%
        \nl\gotocolumn{#1}%
      \fi%
    \fi%
  \fi%
}
\begin{document}
  \begin{tabular}{lcr}
    test \amp test \amp test\nl
    more \amp test \amp stuff\nl
    \gotocolumn{2}test \amp test\nl
    \gotocolumn{3}last\nl
    first \amp \gotocolumn{1}first
  \end{tabular}
\end{document}

Which looks like this.

gotocolumn results

It's not tested very well, so there might be some issues in border cases.

Roelof Spijker
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  • Does this mean that in a normal LaTeX tabular -- without redefining the tab/newline commands -- there's no way for a macro to "find out" where in the table it's being evaluated? – Leah Velleman Dec 21 '11 at 18:04
  • @DanVelleman: You could use the collcell package to process each cell and keep track of the columns. That way the table would look like a normal table. This recent answer question on customize the cell environment in a tabular shows an example usage of collcell. – Peter Grill Dec 22 '11 at 05:52
  • @DanVelleman not as far as I know. Depending on what you mean when you say "redefining the tab/newline commands". Because I'm pretty sure that's exactly what collcell does as well. You can of course redefine the ampersand and \\ to make it look like any other table, while performing the same actions as \amp and \nl. – Roelof Spijker Dec 22 '11 at 12:28