How to get the number of subsections in each section - TeX

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How to get the number of subsections in each section

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samcarter

Back in the days before TL2020 I've been using the `xcntperchap` package to get access to the number of subsections within each section. This was very useful for creating custom tocs in beamer, e.g. here a fancy example using a mindmap:


```
\documentclass{beamer}

\usepackage{tikz}
\usetikzlibrary{mindmap,trees,shadows}

% total number of sections %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\usepackage{totcount}
\newcounter{totalsection}
\regtotcounter{totalsection}

\AtBeginDocument{%
  \pretocmd{\section}{\refstepcounter{totalsection}}{}{}%
}%

% number of subsections per section %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\usepackage{xcntperchap}
\RegisterCounters{section}{subsection}
\newcounter{totalsubsection}
\setcounter{totalsubsection}{0}

% creating automatic label %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% based on https://tex.stackexchange.com/a/386557/36296
\AtBeginSection[]{\label{sec:\thesection}}
\AtBeginSubsection[]{\label{subsec:\thesection:\thesubsection}}
\newcounter{currentsub}
\newcounter{totsection}

\newcommand{\mindtoc}{%
    \centering
    \setcounter{totsection}{\number\totvalue{totalsection}}
  \begin{tikzpicture}[
    grow cyclic,
    concept color=blue!50!black, 
    text=white,
    every node/.style={concept, scale=0.8},
    level 1/.style={%
        sibling angle=360/\thetotsection,
        level distance = 25mm,
        concept color=lime,
        text=black,
    },
    level 2/.style={%
        level distance = 25mm,
        concept color=yellow,
        text=black,
    },      
    ]
        \node {\inserttitle}    [clockwise from=135] child 
        foreach \i in {1,...,\thetotsection}{%
            node{\hyperlink{sec:\i}{\nameref{sec:\i}}
                \setcounter{currentsub}{\ObtainTrackedValueExp[\i]{section}{subsection}}
            }%
            \ifnum\thecurrentsub>0%
                child foreach \j in {1,...,\thecurrentsub}{%
                    node {\hyperlink{subsec:\i:\j}{\nameref{subsec:\i:\j}}} 
                }
            \fi%
        }; 
  \end{tikzpicture}
}

\title{Some Title}

\begin{document}

\begin{frame}
    \frametitle{"Table" of Contents}
    \mindtoc    
\end{frame}

\section{Section One}
\frame{abc}

\section{Section Two}
\frame{abc}

\subsection{subsection a}
\frame{abc}

\subsection{subsection b}
\frame{abc}

\subsection{subsection c}
\frame{abc}

\section{Section Three}
\frame{abc} 

\section{Section Three}
\frame{abc}         

\end{document}
```

However this quick hack no longer works with the current kernel, so I was wondering if there are any alternatives which would give me the number of subsections in each section?

Minimal (non-)working example:

```
\documentclass{beamer}

\usepackage{pgffor}

\usepackage{totcount}
\newcounter{totalsection}
\regtotcounter{totalsection}

\AtBeginDocument{%
  \pretocmd{\section}{\refstepcounter{totalsection}}{}{}%
}%

% number of subsections per section %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\usepackage{xcntperchap}
\RegisterCounters{section}{subsection}
\newcounter{totalsubsection}
\setcounter{totalsubsection}{0}

% creating automatic label %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% based on https://tex.stackexchange.com/a/386557/36296
\AtBeginSection[]{\label{sec:\thesection}}
\AtBeginSubsection[]{\label{subsec:\thesection:\thesubsection}}
\newcounter{currentsub}
\newcounter{totsection}

\newcommand{\mindtoc}{%
\setcounter{totsection}{\number\totvalue{totalsection}}
\foreach \i in {1,...,\thetotsection}{%
    \setcounter{currentsub}{\ObtainTrackedValueExp[\i]{section}{subsection}}
    \nameref{sec:\i} (\thecurrentsub{} subsections)
    
}
}

\title{Some Title}

\begin{document}

\begin{frame}
    \mindtoc    
\end{frame}

\section{Section One}
\frame{zzz}

\section{Section Two}
\frame{zzz}

\subsection{subsection a}
\frame{zzz}

\subsection{subsection b}
\frame{zzz}

\subsection{subsection c}
\frame{zzz}

\section{Section Three}
\frame{zzz}

\section{Section Three}
\frame{zzz}     

\end{document}
```

Top Answer

Phelype Oleinik

The issue is not _exactly_ in the kernel, but in the L3 programming layer.  `\c_zero` was deprecated a while back, because it's name doesn't follow the `expl3` naming conventions: it's an `int`, but it's missing the variable type (so we couldn't have a `\c_zero_fp`, for example).

Christian was very kind to fix most of his packages after this deprecation (even if not actively maintaining them anymore), but `xcntperchap` seems to have been forgotten.

To work around the issue you can, although not really recommended, use:
```
\ExplSyntaxOn
\cs_set_eq:NN \c_zero \c_zero_int
\ExplSyntaxOff
```
anywhere in your preamble to make `\c_zero` be the same as `\c_zero_int`.

---

For completeness, here's a full example (exactly the same as yours, with the lines above added):
```
\documentclass{beamer}


\usepackage{tikz}
\usetikzlibrary{mindmap,trees,shadows}

% total number of sections %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\usepackage{totcount}
\newcounter{totalsection}
\regtotcounter{totalsection}

\AtBeginDocument{%
  \pretocmd{\section}{\refstepcounter{totalsection}}{}{}%
}%

% number of subsections per section %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\ExplSyntaxOn % fix xcntperchap
\cs_set_eq:NN \c_zero \c_zero_int
\ExplSyntaxOff
\usepackage{xcntperchap}
\RegisterCounters{section}{subsection}
\newcounter{totalsubsection}
\setcounter{totalsubsection}{0}

% creating automatic label %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% based on https://tex.stackexchange.com/a/386557/36296
\AtBeginSection[]{\label{sec:\thesection}}
\AtBeginSubsection[]{\label{subsec:\thesection:\thesubsection}}
\newcounter{currentsub}
\newcounter{totsection}

\newcommand{\mindtoc}{%
    \centering
    \setcounter{totsection}{\number\totvalue{totalsection}}
  \begin{tikzpicture}[
    grow cyclic,
    concept color=blue!50!black, 
    text=white,
    every node/.style={concept, scale=0.8},
    level 1/.style={%
        sibling angle=360/\thetotsection,
        level distance = 25mm,
        concept color=lime,
        text=black,
    },
    level 2/.style={%
        level distance = 25mm,
        concept color=yellow,
        text=black,
    },      
    ]
        \node {\inserttitle}    [clockwise from=135] child 
        foreach \i in {1,...,\thetotsection}{%
            node{\hyperlink{sec:\i}{\nameref{sec:\i}}
                \setcounter{currentsub}{\ObtainTrackedValueExp[\i]{section}{subsection}}
            }%
            \ifnum\thecurrentsub>0%
                child foreach \j in {1,...,\thecurrentsub}{%
                    node {\hyperlink{subsec:\i:\j}{\nameref{subsec:\i:\j}}} 
                }
            \fi%
        }; 
  \end{tikzpicture}
}
\title{Some Title}

\begin{document}

% \tracingall
\begin{frame}
    \frametitle{"Table" of Contents}
    \mindtoc    
\end{frame}

\section{Section One}
\frame{abc}

\section{Section Two}
\frame{abc}

\subsection{subsection a}
\frame{abc}

\subsection{subsection b}
\frame{abc}

\subsection{subsection c}
\frame{abc}

\section{Section Three}
\frame{abc}

\section{Section Three}
\frame{abc}

\end{document}
```

1 Answer