combine enumeration of chapters

at the beginning of one part of my document I've got a tabular with some values and in the chapters afterwards I'll explain them. Some values need to be combined; so the chapters have to be enumerated eg. that way:

1. A
2. B
3. - 5. C
6. - 7. D
8. E


I think of something like defining an alternate chapter-command \chapterA.

For instance:

\chapter{A}
\chapter{B}
\chapterA{3}{C} % combine 3 values
\chapterA{2}{D} % combine 2 values
\chapter{E}


What does this command have to look like?

I found this but couldn't manage to apply it to the \chapter command.

-

One option using titlesec; the command \standardchapter produces a "normal" heading; \combinedchapter produces a heading in each the numbering has the form <number>.-- <number>+#1, where #1 is the integer in the mandatory argument:

\documentclass{book}
\usepackage{titlesec}

\newcommand\standardchapter{%
\titleformat{\chapter}[block]
{\normalfont\huge\bfseries}{\thechapter.}{1em}{}
}
\newcommand\combinedchapter[1]{%
\titleformat{\chapter}[block]
}

\begin{document}

\let\cleardoublepage\relax% just for the example

\standardchapter
\chapter{A}
\chapter{B}
\combinedchapter{2}
\chapter{C}
\combinedchapter{3}
\chapter{D}
\standardchapter
\chapter{E}

\end{document}


-

The following example defines \chapterA with a range as chapter number. Also chapters inside the appendix are supported. Because of the longer numbers, the table of contents is adjusted accordingly.

\documentclass{scrreprt}

\let\savedthechapter\thechapter
\let\orgchapter\chapter
\renewcommand*{\chapter}{%
\let\thechapter\savedthechapter
\orgchapter
}
\newcommand*{\chapterA}[1]{%
\stepcounter{chapter}%
\edef\thechapterauxA{\savedthechapter}%
\edef\thechapterauxB{\savedthechapter}%
\edef\thechapter{\thechapterauxA.--\thechapterauxB}%
\orgchapter
}

% \appendix changes \thechapter for uppercase letters
\makeatletter
\global\let\savedthechapter\thechapter
}
\makeatother

% patch \l@chapter to get room for the chapter number
\usepackage{etoolbox}
\makeatletter
\patchcmd{\l@chapter}{%
\setlength\@tempdima{1.5em}%
}{%
\setlength\@tempdima{3em}%
}{}{\errmessage{Patching \string\l@chapter\space failed}}
\patchcmd{\l@section}{{1.5em}}{{3em}}%
{}{\errmessage{Patching \string\l@section\space failed}}
\patchcmd{\l@subsection}{{3.8em}}{{5.3em}}%
{}{\errmessage{Patching \string\l@subsection\space failed}}
% analog: subsubsection, paragraph, subparagraph, ...
\makeatother

\begin{document}
\tableofcontents
\chapter{A}
\chapter{B}
\chapterA{3}{C} % combine 3 values
\chapterA{2}{D} % combine 2 values
\chapter{E}
\section{Section}
\subsection{Subsection}
\appendix
\chapter{Appendix 1}
\chapterA{3}{Appendix 2-4}
\chapter{Appendix 5}
\end{document}


-