newcommand for \end{tabular}\\? Getting around syntax and escape

Question

I have a table-making program that creates tables for me. One problem, however, is that it isn't written very well.

For example, I would like it to make a table that looks like this:

\begin{tabular}{|l|lll|l|}
\cline{1-1} \cline{5-5}
id & x                      & y                      & y & sum \\ \cline{1-1} \cline{5-5} 
a  & 1                      & 2                      & 3 & 6   \\ \cline{1-1} \cline{5-5} 
b  & 1                      & 2                      & . & 3   \\ \hline
c  & \multicolumn{1}{l|}{.} & \multicolumn{1}{l|}{.} & . & .   \\ \hline
\end{tabular}

Sometimes, however, it adds to backslashes to the end of the end{tabular} command, which reads end{tabular}\\. This throws an error in some environments, like threeparttable and center.

I have edited the source code for this program on my own machine, and emailed an unresponsive maintainer. I have an upcoming project where I will need to share this code with multiple coworkers across multiple computers, and i can't have everyone find the exact command to change in the code of the package. This isn't even beginning to consider errors with reproducability in general.

I realized that good fix for this would be to just have Latex read the command \end{tabular}\\ as end{tabular}. But I can't get the syntax to work when I try to define my own command. Can someone help me create this definition? I do not understand why \newcommand{\end{tabular}\\}{\end{tabular}} doesn't work.

EDIT:

I have added a MWE. The following code will not compile using ShareLatex. An error pops up in the blank line after end{tabular}\\ saying "There is no line to end here". The second chunk of code, which ends with end{tabular} (no backslashes) compiles fine.

\documentclass[12pt]{article}
\usepackage[a4paper, margin = .5in]{geometry}
\usepackage{pdflscape}
\usepackage{threeparttable}
\begin{document} 




\begin{table}
\caption{My test table}
\begin{center}
\begin{threeparttable}
\small
\begin{tabular}{lll}
a    & b    & c    \\
2    & 3    & 4    \\
this & that & here
\end{tabular}\\

\begin{tablenotes}
\item 
\end{tablenotes}
\end{threeparttable}
\end{center}
\end{table}

\end{document}

This is the second block of code, the one that runs.

\documentclass[12pt]{article}
\usepackage[a4paper, margin = .5in]{geometry}
\usepackage{pdflscape}
\usepackage{threeparttable}
\begin{document} 




\begin{table}
\caption{My test table}
\begin{center}
\begin{threeparttable}
\small
\begin{tabular}{lll}
a    & b    & c    \\
2    & 3    & 4    \\
this & that & here
\end{tabular}

\begin{tablenotes}
\item 
\end{tablenotes}
\end{threeparttable}
\end{center}
\end{table}

\end{document}

Can you provide code showing where the use-case throws an error? — Werner, Dec 14 '17 at 06:52

score 2 · Accepted Answer · answered Dec 16 '17 at 05:56

You cannot get rid of this error by redefining \tabular, of which the \begin{tabular} and \end{tabular} is just an extension. That's because the errative \\ just occurs occasionally.

You also shouldn't try to solve this by redefining \\, because such a definition would have to poke a lot into TeX internals.

I think your best options are

find someone to fix this bug in the table generator and get it officially released,
create an inofficial patch for the latest release and distribute that to your team, or
try to find a workaround for that bug, such as optimizing the source file that contains the table prior to compilation

You could also post-process the output with a small script that removes any trailing \\ after tabular.

Thank you. I will look into my program's generic read/write functions to do a string replace immediately after saving the file. — genauguy, Dec 19 '17 at 19:15

score 0 · Answer 2 · answered Jan 02 '18 at 22:06

You could use LuaLaTeX and (a) set up a function that changes all instances of \end{tabular}\\ in the text to \end{tabular} "on the fly" and (b) assign this function to the so-called process_input_buffer callback, which does its work at a very early stage of processing, before (La)TeX does any of its usual work.

% !TEX TS-program = lualatex
\documentclass{article}

\usepackage{threeparttable}

\usepackage{luacode}
\begin{luacode}
function removetabularbs ( line )
    return string.gsub ( line, "\\end{tabular}\\\\", "\\end{tabular}" )
end
luatexbase.add_to_callback ( "process_input_buffer", removetabularbs, "removetabularbs" )
\end{luacode}

\begin{document} 

\begin{threeparttable}
  \begin{tabular}{ l l l }
    a    & b    & c    \\
    2    & 3    & 4    \\
    this & that & here
  \end{tabular}\\
  \begin{tablenotes}
    \item Something
  \end{tablenotes}
\end{threeparttable}

\end{document}

This way you're still processing the source without having to change the code.

newcommand for \end{tabular}\\? Getting around syntax and escape

2 Answers2