How do I use < and > column specifiers?

Question

I can't quite figure it out. I'd like to be able to process the entries in a table, but > and < aren't (quite) acting as I expect them to. Here's a repro:

\documentclass{article}
\usepackage{array}
\newcolumntype{Z}{>{\foo}c<{\bar}}
\def\foo#1\bar{foo #1 bar}
\begin{document}
\begin{tabular}{ZZZZ}
A & B & C & D \\
E & F & G & H
\end{tabular}
\end{document}

When I run this through xelatex I get the following output:

$ xelatex repro
This is XeTeX, Version 3.14159265-2.6-0.99998 (TeX Live 2017/MacPorts 2017_0) (preloaded format=xelatex)
 restricted \write18 enabled.
entering extended mode
(./repro.tex
LaTeX2e <2017-04-15>
Babel <3.10> and hyphenation patterns for 5 language(s) loaded.
(/opt/local/share/texmf-texlive/tex/latex/base/article.cls
Document Class: article 2014/09/29 v1.4h Standard LaTeX document class
(/opt/local/share/texmf-texlive/tex/latex/base/size10.clo))
(/opt/local/share/texmf-texlive/tex/latex/tools/array.sty) (./repro.aux)
! Misplaced \cr.
\reserved@c ->\ifnum 0=`{}\fi \cr 

l.8 E &
        F & G & H
?

Oddly, it works as I expect if I use {ZZcc} as the preamble, but that must surely be only lucky. How do I use > and < column specifiers to process table entries?

@AlanMunn Thanks, collcell (mentioned in the answers to that question) looks like it will help! — ruds, Jul 31 '17 at 19:46
Yes, collcell is a great package for this kind of thing. It's not needed for simple things, but for more complicated processing of the cell it makes life a lot easier. — Alan Munn, Jul 31 '17 at 19:48

score 3 · Accepted Answer · answered Jul 31 '17 at 19:39

3

The last column is not so easy to catch, because it is not ended by &. Then \foo gets all the stuff up to the next & including \\.

A workaround is to add a dummy last column:

\documentclass{article}
\usepackage{array}
\newcolumntype{Z}{>{\foo}c<{\bar}}
\def\foo#1\bar{foo #1 bar}
\begin{document}
\begin{tabular}{ZZZZ@{}c}
A & B & C & D &\\
E & F & G & H &
\end{tabular}
\end{document}

answered Jul 31 '17 at 19:39

Heiko Oberdiek

271,626

Thanks, that explains it! Seems like something that should be mentioned in Mittelbach and Carlisle's "A new implementation of LaTeX's tabular and array environment" but at least now I understand the problem. – ruds Jul 31 '17 at 19:48

How do I use < and > column specifiers?

1 Answers1