Macro limited in scope to the tabular cell in which it is invoked?

Question

How do I reuse cell delimiter of a tabular environment (usually ampersand) for delimiting a macro parameter?

Like this (which unfortunately doesn't work):

\def\mymacro#1&{#1}

...

\begin{tabular}
Hello & \mymacro out & there \\
\end{tabular}

where \mymacro shall only apply to out.

I'd rather not use curly braces in this particular case to delimit the parameter value.

Also, I should mention that a space won't work either as there might be spaces in the parameter value as well.

I'm not sure I understand. Your macro has only one argument. What is there to delimit? What role is the ampersand supposed to play in this? — jub0bs, May 29 '13 at 13:52
I see. I'd like the macro to apply for the whole cell content of a tabular which it is in without having to use curly braces surrounding that content. — Hendrik Wiese, May 29 '13 at 13:55
Now I understand. I think you should add that clarification in your question. — jub0bs, May 29 '13 at 13:58
This might be related to your problem: Easiest way to delete a column — egreg, May 29 '13 at 15:45

David Carlisle · Answer 1 · 2017-03-19T08:58:55.597

5

The exact rules of how macro expansion interacts with table scanning are somewhat arcane but in this instance you can do this:

enter image description here

\documentclass{article}


\begin{document}

or a version that works even if not the first token in the cell.

enter image description here

\def\mymacro#1&{\fbox{#1\unskip}&}


\documentclass{article}


\begin{document}

\def\mymacro{\relax\mymacrox}
\def\mymacrox#1\unskip{\fbox{#1\unskip}}

\begin{tabular}{ccc}
Hello &aaa \mymacro out & there \\
Hello &\mymacro out & there \\
\end{tabular}

\end{document}

\begin{tabular}{ccc}
Hello & \mymacro out & there \\
\end{tabular}

\end{document}

edited Mar 19 '17 at 08:58

answered May 29 '13 at 14:20

David Carlisle

757,742

This only works if \mymacro is the first (non-space) token in the cell. In general, the OP is right that it will break. – Bruno Le Floch May 29 '13 at 14:22
Yeah, it will suffice for now. If there's another more flexible solution that does not require to be the first non-space token, as mentioned by @BrunoLeFloch, I'll be grateful if someone could explain that as well. – Hendrik Wiese May 29 '13 at 14:44
@HendrikWiese you can make more general versions or, simpler in some ways versions that work with the >{\myfoo}c<{\endmyfoo} syntax of array package, but they all have quirks and edge cases... – David Carlisle May 29 '13 at 15:37
@BrunoLeFloch updated with alternative version that works mid cell. – David Carlisle May 29 '13 at 15:42
@HendrikWiese updated – David Carlisle May 29 '13 at 15:43

Macro limited in scope to the tabular cell in which it is invoked?

1 Answers1