How to ignore some items in a numbering environment?

Question

I have a environment to number the paragraphs in it, if I have to ignore some paragraphs in the environment which needn't be numbered, eg: I want to ignore numbering of the \lipsum[6-7], how to make it?

The whole codes of the environment are here:

 \documentclass{book}
\usepackage{mparhack}   % get marginpars to always show up on the correct side (need to compile twice)
\usepackage{lipsum}     % for dummy text

% change this to get the formatting you want
\newcommand{\parnum}{\bfseries\arabic{parcount}}
\newcounter{parcount}
\newenvironment{parnumbers}{%
\par%
   \everypar{\stepcounter{parcount}\leavevmode\marginpar[\hfill\parnum]
{\parnum}}%
\setcounter{parcount}{0}%to restart numbering in every environment
}{}

\begin{document}
\begin{parnumbers}
\lipsum[1-4]
\end{parnumbers}

\begin{parnumbers}
\lipsum[5-8]
\end{parnumbers}

\begin{parnumbers}
\lipsum[9-10]
\end{parnumbers}

\end{document}

Answer 1

You can define a starred version of parnumbers environment like (My method may be rude though)

\newenvironment{parnumbers*}{%
\par%
   \everypar{\stepcounter{parcount}\leavevmode\marginpar[\hfill]
{}}%
\setcounter{parcount}{0}%to restart numbering in every environment
}{}

Then

\begin{parnumbers}
\lipsum[5]
\begin{parnumbers*}
\lipsum[6-7]
\end{parnumbers*}
\lipsum[8]
\end{parnumbers}

should do the job.

The complete MWE:

\documentclass{book}
\usepackage{mparhack}   % get marginpars to always show up on the correct side (need to compile twice)
\usepackage{lipsum}     % for dummy text

% change this to get the formatting you want
\newcommand{\parnum}{\bfseries\arabic{parcount}}
\newcounter{parcount}
\newenvironment{parnumbers}{%
\par%
   \everypar{\stepcounter{parcount}\leavevmode\marginpar[\hfill\parnum]
{\parnum}}%
\setcounter{parcount}{0}%to restart numbering in every environment
}{}

\newenvironment{parnumbers*}{%
\par%
   \everypar{\stepcounter{parcount}\leavevmode\marginpar[\hfill]
{}}%
\setcounter{parcount}{0}%to restart numbering in every environment
}{}

\begin{document}
\begin{parnumbers}
\lipsum[1-4]
\end{parnumbers}

\begin{parnumbers}
\lipsum[5]
\begin{parnumbers*}
\lipsum[6-7]
\end{parnumbers*}
\lipsum[8]
\end{parnumbers}

\begin{parnumbers}
\lipsum[9-10]
\end{parnumbers}

\end{document}

Answer 2

I improve your codes as follows:

\newenvironment{parnumbers*}{%to ignore some items 
\par
\everypar{\leavevmode\marginpar[\hfill]
{}}%
}{}

So as I wanted, lipsum 5's number is 1 lipsum 8's number is 2 lipsum 6-7 are ignored.

The last question is how to make it by a command, not such a environment?

The complete MWE:

\documentclass{book}
 \usepackage{mparhack}   % get marginpars to always show up on the correct side (need to compile twice)
\usepackage{lipsum}     % for dummy text

% change this to get the formatting you want
\newcommand{\parnum}{\bfseries\arabic{parcount}}
\newcounter{parcount}
\newenvironment{parnumbers}{%
\par%
   \everypar{\stepcounter{parcount}\leavevmode\marginpar[\hfill\parnum]
{\parnum}}%
\setcounter{parcount}{0}%to restart numbering in every environment
}{}

\newenvironment{parnumbers*}{%
\par%
   \everypar{\leavevmode\marginpar[\hfill]
{}}%

}{}

\begin{document}
\begin{parnumbers}
\lipsum[1-4]
\end{parnumbers}

\begin{parnumbers}
\lipsum[5]
\begin{parnumbers*}
\lipsum[6-7]
\end{parnumbers*}
\lipsum[8]
\end{parnumbers}

\begin{parnumbers}
\lipsum[9-10]
\end{parnumbers}

\end{document}