Display environment differently for one use vs. two

Question

My issue can be boiled down to this:

\documentclass[10pt,oneside]{article}
\usepackage{enumitem}

\newenvironment{mygroup}{
  \vspace{.15in}

  \textbf{\large MyGroup Heading}
}{
}

\newenvironment{mylist}[1]{
  \newcommand{\myitem}[1]{
    \item ##1:%
  }

  \vspace{.12in}

  \emph{\fontsize{11}{11}\selectfont#1}
  \begin{itemize}[noitemsep,nolistsep]
}{
  \end{itemize}
}

\begin{document}
  \begin{mygroup}
    \begin{mylist}{subheading 1}
      \myitem{item 1} item 1 content
      \myitem{item 2} item 2 content
    \end{mylist}
    \begin{mylist}{subheading 2}
      \myitem{another item} content
    \end{mylist}
  \end{mygroup}
\end{document}

Currently, I display subheadings no matter how many mylists there are inside a mygroup. How do I make it so that subheadings only display if there are two or more mylists in a mygroup, and if there is only one, its subheading is not displayed?

Answer 1

This uses my cntperchap package which stores total counters per chapter level, but this could be set to another counter as well. Here, the mygroup is set as tracklevel.

The \GetStoredCounterValue{mylist} gets the value from a previous run and stores it to cps@@tempstoragecounter counter, which can then be queried with \ifnumgreater (which is from etoolbox, but this package is loaded by cntperchap already.

(Side note: I have to change the documentation and the \GetStoredCounterValue approach in the next release -- it's not convenient so far.)

---

\documentclass[10pt,oneside]{article}
\usepackage{enumitem}

\newcounter{mygroup}
\usepackage[tracklevel=mygroup]{cntperchap}

\newcounter{mylist} % track the lists

\RegisterCounters{mylist} % prepare for tracking

\makeatletter

\newenvironment{mygroup}{%
  \vspace{.15in}
  \textbf{\large MyGroup Heading}
}{
}

\makeatother

\newenvironment{mylist}[1]{%
  \stepcounter{mylist}%
  \GetStoredCounterValue{mylist}%
  \newcommand{\myitem}[1]{%
    \item ##1:%
  }

  \vspace{.12in}

  \ifnumgreater{\value{cps@@tempcounterstorage}}{1}{%
    \emph{\fontsize{11}{11}\selectfont#1}
  }{}%

  \begin{itemize}[noitemsep,nolistsep]
  }{%
  \end{itemize}
}

\begin{document}
  \begin{mygroup}
    \begin{mylist}{subheading 1}
      \myitem{item 1} item 1 content
      \myitem{item 2} item 2 content
    \end{mylist}
    \begin{mylist}{subheading 2}
      \myitem{another item} content
    \end{mylist}
  \end{mygroup}

  \begin{mygroup}
   \begin{mylist}{subheading 1 which isn't displayed}
     \myitem{item 1} Just one list, part 1
     \myitem{item 2} Just one list, part 2
   \end{mylist}
 \end{mygroup}

\end{document}

Answer 2

After meditating on Christian's answer and doing a bit more googling, I came up with a solution that uses the totcount package instead:

\documentclass[10pt,oneside]{article}
\usepackage{enumitem}
\usepackage{totcount}

\newcounter{mygroupcount}

\newenvironment{mygroup}{
  \stepcounter{mygroupcount}
  \edef\mycount{mycount\alph{mygroupcount}}
  \expandafter\newtotcounter\expandafter{\mycount}
  \vspace{.15in}

  \textbf{\large MyGroup Heading}
}{
}

\newenvironment{mylist}[1]{
  \stepcounter{\mycount}
  \newcommand{\myitem}[1]{
    \item ##1:%
  }

  \vspace{.12in}

  \ifnum 1<\totvalue{\mycount}
    \emph{\fontsize{11}{11}\selectfont#1}
  \fi
  \begin{itemize}[noitemsep,nolistsep]
}{
  \end{itemize}
}

\begin{document}
  \begin{mygroup}
    \begin{mylist}{subheading 1}
      \myitem{item 1} item 1 content
      \myitem{item 2} item 2 content
    \end{mylist}
    \begin{mylist}{subheading 2}
      \myitem{another item} content
    \end{mylist}
  \end{mygroup}
  \begin{mygroup}
    \begin{mylist}{subheading 1 - not shown}
      \myitem{item 1} item 1 content
      \myitem{item 2} item 2 content
    \end{mylist}
  \end{mygroup}
\end{document}

As Christian's solution is a bit simpler, I would prefer to use that, but for an older TeX distribution, this works.