Repeating Numbered Items in Beamer

Question

I want to be able to repeat a numbered item from an earlier slide under the same number. I know I can do the following, if the item I want to repeat is from the immediately preceding slide:

\documentclass[pdf]{beamer}
   \usepackage[utf8]{inputenc}
   \usepackage{tipa}
   \usecolortheme{beaver}
   \setbeamercovered{highly dynamic}
   \mode<presentation>{}
       \newcounter{saveenumi}
       \newcommand{\seti}{\setcounter{saveenumi}{\value{enumi}}}
       \newcommand{\conti}{\setcounter{enumi}{\value{saveenumi}}}

       \resetcounteronoverlays{saveenumi}
       \AtBeginSection[]
      {
       \begin{frame}<beamer>
       \frametitle{}
       \tableofcontents[currentsection]
       \end{frame}
      }
 \begin{document}
 \begin{frame}
     \begin{enumerate}
     \item First.
     \seti
     \end{enumerate}   
\end{frame}
\begin{frame}
    \begin{enumerate}
    \conti
    \item Second.
    \end{enumerate}    
\end{frame}
\begin{frame}
    \begin{enumerate}
    \conti
    \item Second again.
    \seti
    \end{enumerate} 
\end{frame} \end{document}

But I want to be able to repeat an arbitrary item from an arbitrary slide. I also know I could do this:

 \documentclass[pdf]{beamer}
   \usepackage[utf8]{inputenc}
   \usepackage{tipa}
   \usecolortheme{beaver}
   \setbeamercovered{highly dynamic}
   \mode<presentation>{}

      \begin{document}
         \begin{frame}
            \begin{enumerate}
            \item First.\label{1}
            \end{enumerate}
         \end{frame}
        \begin{frame}
            \begin{itemize}
            \item[\ref{1}] First again.
            \end{itemize}
        \end{frame}
      \end{document}

But that is clunky and often ugly, as \item[\ref{1}] doesn't automatically preserve the style and alignment of the numbering labels from previous slides.

Answer 1

You could use the refcount package to have an expandable reference number that you can play with. This allows you to use the tricks of your first code in the last one.

\documentclass[pdf]{beamer}
\usepackage[utf8]{inputenc}
\usepackage{tipa}
\usepackage{refcount}
\usecolortheme{beaver}
\setbeamercovered{highly dynamic}
\mode<presentation>{}

\begin{document}
   \begin{frame}
      \begin{enumerate}
      \item First.\label{1}
      \item Second.\label{2}
      \item Third.\label{3}
      \end{enumerate}
   \end{frame}
  \begin{frame}
      \begin{enumerate}\setcounter{enumi}{\the\numexpr\getrefnumber{1}-1}
      \item First again.\setcounter{enumi}{\the\numexpr\getrefnumber{3}-1}
      \item Third again.
      \end{enumerate}
  \end{frame}
\end{document}

Obviously you can cast this into a macro.

\documentclass[pdf]{beamer}
\usepackage[utf8]{inputenc}
\usepackage{tipa}
\usepackage{refcount}
\usecolortheme{beaver}
\setbeamercovered{highly dynamic}
\mode<presentation>{}
\newcommand{\repeateditem}[1]{%
\setcounter{enumi}{\the\numexpr\getrefnumber{#1}-1}%
\item}
\begin{document}
   \begin{frame}
      \begin{enumerate}
      \item First.\label{1}
      \item Second.\label{2}
      \item Third.\label{3}
      \end{enumerate}
   \end{frame}
  \begin{frame}
      \begin{enumerate}
      \repeateditem{1} First again.
      \repeateditem{3} Third again.
      \end{enumerate}
  \end{frame}
\end{document}

Answer 2

Maybe I didn't get it right, but why another list in another frame?

\documentclass{beamer}
\geometry{paperheight=1.5in,paperwidth=2in}
\begin{document}
   \begin{frame}
      \begin{enumerate}
      \item \only<1>{First}\only<2>{First again}\label{1}
      \item<1> Second\label{2}
      \item \only<1>{Third}\only<2>{Third again}\label{3}
      \end{enumerate}
   \end{frame}
\end{document}

For non contiguous slides and without the space for the lost item:

\documentclass{beamer}
\geometry{paperheight=1.5in,paperwidth=2in}
\begin{document}
   \begin{frame}<1>[label=xxx]
      \begin{enumerate}
      \item \only<1>{First}\only<2>{First again}\label{1}
      \only<1>{\item Second\label{2}}\only<2>{\stepcounter{enumi}}
      \item \only<1>{Third}\only<2>{Third again}\label{3}
      \end{enumerate}
   \end{frame}

\begin{frame}
    Another frame
\end{frame}

\againframe<2>{xxx} 

\end{document}