align columns in multiple tables

Question

I am trying to align the columns of multiple tables. I know I can use p column format to fix column widths but I would prefer that TeX automatically figure out the widths for me. I was hoping to:

1. output one table with all rows of each subsequent table so that the column widths of the combined table would be automatically good for all the subsequent tables
2. then output each subsequent table using the same settings and
3. figure out some way in which the first combined table could be generated but not visible.

Here is my attempt. The first combined table uses \savetabu to save the settings and then each subsequent table uses \usetabu to retrieve them. Unfortunately this does not work as I had hoped. The columns do not line up as the output below (after the code) shows. Does anyone have a method of accomplishing this?

\documentclass{article}

\usepackage{tabu}
\begin{document}

Output both tables together as one table and then output each
individual table.  We had hoped that this would cause the subsequent
tables to be the same width as the first since the first contains all
columns of the subsequent tables but it seems that that does not work.

\begin{center}
\begin{tabu}{ll}\savetabu{mytabu2}
1 & 2 \\
3 & 4 \\
abcdefghijklmnopqrstuvwxyz & 10 \\
5 & 6 \\
\end{tabu}
\end{center}

\begin{center}
\begin{tabu}{\usetabu{mytabu2}}
1 & 2 \\
3 & 4 \\
\end{tabu}
\end{center}

\begin{center}
\begin{tabu}{\usetabu{mytabu2}}
abcdefghijklmnopqrstuvwxyz & 10 \\
5 & 6 \\
\end{tabu}
\end{center}

\end{document}

Here is the output:

Answer 1

What you describe is basically what longtable does internally so that the various parts of the table line up, so it is fairly easy to use longtable but redefine things so the two tables share longtable width data:

\documentclass{article}

\usepackage{longtable}
\makeatletter
\def\dontchopLT{\let\LT@entry@chop\relax}
\def\resumeLT{%
\let\zzz\stepcounter
\def\yyy{LT@tables}
\def\stepcounter##1{%
  \def\xxx{##1}%
  \ifx\xxx\yyy\else\zzz{##1}\fi}}
\makeatother

\begin{document}

Output both tables together as one table and then output each
individual table.  We had hoped that this would cause the subsequent
tables to be the same width as the first since the first contains all
columns of the subsequent tables but it seems that that does not work.




\noindent X\dotfill X

{\dontchopLT
\begin{longtable}{ll}
1 & 2 \\
3 & 4 \\
\end{longtable}}

\noindent X\dotfill X





{\resumeLT
\begin{longtable}{ll}
abcdefghijklmnopqrstuvwxyz & 10 \\
5 & 6 \\
\end{longtable}}

\end{document}

Answer 2

The tabu environment will need to use the X columns in order to be able to scale them and remember the calculations with savetabu.

since you do not want the table to occupy the full line width, you can use the spread definition with a value a 0pt and have your X columns with a negative coefficient:

\begin{tabu} spread 0pt  {|X[-1]|X[-1]|}\savetabu{mytabu2}
1 & 2 \\
3 & 4 \\
abcdefghijklmnopqrstuvwxyz & 10 \\
5 & 6 \\
\end{tabu}
\end{center}

\begin{center}
\begin{tabu}{\usetabu{mytabu2}}
1 & 2 \\
3 & 4 \\
\end{tabu}
\end{center}

\begin{center}
\begin{tabu}{\usetabu{mytabu2}}
abcdefghijklmnopqrstuvwxyz & 10 \\
5 & 6 \\
\end{tabu}