alternating numbering within sections

Question

I am typesetting a book which is divided into paragraphs (sections), which are numbered continuously through the whole book, and which contain some tables. Tables must be numbered with the same number as the section within which they are located. Thus, "Table 23" is immediately recognizable as the being located in the Section 23.

However, some sections contain more than one tables. I need them to be numbered with a sequential number added to the section number, restarting per each section.

E.g.: Tables 46.1 and Table 46.2 stand both within the Section 46, while Tables 120.1, 120.2 and 120.3 are located in the Section 120.

But, importantly, if there is only one Table in a Section, its number must remain simply the same as the Section number, without the trailing ".1".

Can I achieve this automatically?

Answer 1

The following seems to do the trick, at least using the amsbook document class. For other document classes it might need some tweaking (this is why it is always good to give a minimal working example).

The basic idea is that whenever a section is started (or at the end of the document) the number of tables in the previous section is saved to the aux file with a label of the form TablesInSection<section#>. Then the \thetable command uses the \setcounterref command from the refcount package to check to see if the section contains more than one table. If it does, then the table number is printed with the section number and otherwise only the section number is printed.

As the number of tables in each section is being saved in the aux file you will need to run (pdf)latex twice each time the number of tables in any section changes. I have not checked to see what happens if the \section command is used with an optional argument, so it is quite likely this will need tweaking. If you are using chapters then sections should also be numbered inside chapters, although you could hack around this.

Here is the output:

and here is the code:

\documentclass{amsbook}
\usepackage{etoolbox}
\usepackage{refcount}
\numberwithin{table}{section}
\makeatletter
% write a label to the aux file
\newrobustcmd{\WriteLabel}[2]{%
% use the following if hyperref is loaded
%   \immediate\write\@auxout{\string\newlabel{#1}{{#2}{}{}{#1.#2}{}}}
    \immediate\write\@auxout{\string\newlabel{#1}{{#2}{\thepage}}}%
}
\makeatother

\newcommand\savesectiontablenumber{%
  \ifnum\value{section}>0%
    \ifnum\value{table}>0%
      \WriteLabel{TablesInSection\thesection}{\arabic{table}}%
    \fi%
  \fi%
}
\preto\section\savesectiontablenumber
\AtEndDocument{\savesectiontablenumber}
\newcounter{tablechecker}
\renewcommand\thetable{%
  \setcounterref{tablechecker}{TablesInSection\thesection}
  \ifnum\thetablechecker>1
    \thesection.\arabic{table}%
  \else\thesection%
  \fi%
}

\begin{document}

\section{Section one}
  \begin{table}[h]\caption{A table}\label{single}
A table
\end{table}

\section{Section one}
  \begin{table}[h]\caption{First table}\label{one}
First table
\end{table}
\begin{table}[h]\caption{Second table}\label{two}
Second table
\end{table}

\end{document}