List of Figures + Beamer? (followup)

Question

I'm interested in making a list of figures in Beamer so that I don't have to cite each image in its caption and I can save slide space. The following example (per users Marco Daniel and Carsten) is working almost perfectly for what I want to do; I can put the source as the optional argument in the caption and have it print on the LOF but not on the frame with the figure. However I'm finding that in frames that are divided into multiple slides end up printing any figures they have multiple times (once per slide) in the LOF.

\documentclass{beamer}
\usetheme{PaloAlto}
\usepackage{ifthen}

\makeatletter
\AtEndDocument{%
    \clearpage
    \beamer@tempcount=\c@page\advance\beamer@tempcount by -1%
    \if@filesw
    \newwrite\tf@lof
    \immediate\openout\tf@lof\jobname.lof\relax
    \newwrite\tf@lot
    \immediate\openout\tf@lot\jobname.lot\relax
    \fi
}
\long\def\beamer@makecaption#1#2#3#4{%
    \def\insertcaptionname{\csname#1name\endcsname}%
    \def\insertcaptionnumber{\csname the#1\endcsname}%
    \edef\insertframenumber{\theframenumber}%
    \ifthenelse{\equal{#3}{\empty}}{%  
        \def\insertlistcaption{#2}%
    }{%
        \def\insertlistcaption{#3}%
    }
    \def\insertsource{#4}%
    \def\insertcaption{#2}%
    \ifthenelse{\equal{#1}{figure}}{%  
        \addtocontents{lof} 
{\protect\listoffigureformat{\insertcaptionnumber}{\insertlistcaption} 
{\insertframenumber}{\insertsource}}{}{}%
    }{}
    \ifthenelse{\equal{#1}{table}}{%  
        \addtocontents{lot}{\protect\listoftableformat{\insertcaptionnumber} 
{\insertlistcaption}{\insertframenumber}}{}{}%
    }{}
    \nobreak\vskip\abovecaptionskip\nobreak
    \sbox\@tempboxa{\usebeamertemplate**{caption}}%
    \ifdim \wd\@tempboxa >\hsize
    \usebeamertemplate**{caption}\par
    \else
    \global \@minipagefalse
    \hb@xt@\hsize{\hfil\box\@tempboxa\hfil}%
    \fi
    \nobreak\vskip\belowcaptionskip\nobreak%
}
\def\listoffigureformat#1#2#3#4{%
    \makebox[2ex][r]{#1}%
    \hspace{1ex}%
    {\usebeamercolor[fg]{bibliography entry author} #2}%
    \ifthenelse{\equal{#4}{\empty}}{}{ -- #4}%
    \dotfill%
    \makebox[2ex][r]{#3}\par%
}
\def\listoffigures{%
    \setlength{\leftskip}{3ex}
    \setlength{\parindent}{-3ex}
    \@starttoc{lof}%
}
\def\listoftableformat#1#2#3{\makebox[2ex][r] 
{#1}\hspace{1ex}#2\dotfill\makebox[2ex][r]{#3}\par}
\def\listoftables{%
    \setlength{\leftskip}{3ex}
    \setlength{\parindent}{-3ex}
    \@starttoc{lot}%
}
\long\def\@caption#1[#2]#3{
    \par\nobreak
    \begingroup
    \@parboxrestore
    \if@minipage
    \@setminipage
    \fi
    \beamer@makecaption{#1}{\ignorespaces #3}{\ignorespaces #3} 
{\ignorespaces #2}\par\nobreak
    \endgroup}
\makeatother

\begin{document}

\begin{frame}{Frame}
\begin{figure}
\mbox{A}
\caption[citation]{The letter 'A'}
\end{figure}
\begin{itemize}
    \item<1-> an item
    \item<2-> another item
    \item<3-> a third item
\end{itemize}
\end{frame}
\begin{frame}{List of Figures}
\listoffigures
\end{frame}

\end{document}

It would seem simple enough to write a test that determines whether an entry is already in the list of figures and doesn't add the new entry if an old one matches it, however I'm fairly new to coding and don't know how to approach this in LaTeX. Could somebody please help me out?

Answer 1

Quick hack:

\documentclass{beamer}
\usetheme{PaloAlto}
\usepackage{ifthen}

\makeatletter
\AtEndDocument{%
    \clearpage
    \beamer@tempcount=\c@page\advance\beamer@tempcount by -1%
    \if@filesw
    \newwrite\tf@lof
    \immediate\openout\tf@lof\jobname.lof\relax
    \newwrite\tf@lot
    \immediate\openout\tf@lot\jobname.lot\relax
    \fi
}
\long\def\beamer@makecaption#1#2#3#4{%
    \def\insertcaptionname{\csname#1name\endcsname}%
    \def\insertcaptionnumber{\csname the#1\endcsname}%
    \edef\insertframenumber{\theframenumber}%
    \ifthenelse{\equal{#3}{\empty}}{%  
        \def\insertlistcaption{#2}%
    }{%
        \def\insertlistcaption{#3}%
    }
    \def\insertsource{#4}%
    \def\insertcaption{#2}%
    \ifthenelse{\equal{#1}{figure}}{%  
    \only<+>{
        \addtocontents{lof} 
{\protect\listoffigureformat{\insertcaptionnumber}{\insertlistcaption} 
{\insertframenumber}{\insertsource}}{}{}%
    }}{}
    \ifthenelse{\equal{#1}{table}}{%  
        \addtocontents{lot}{\protect\listoftableformat{\insertcaptionnumber} 
{\insertlistcaption}{\insertframenumber}}{}{}%
    }{}
    \nobreak\vskip\abovecaptionskip\nobreak
    \sbox\@tempboxa{\usebeamertemplate**{caption}}%
    \ifdim \wd\@tempboxa >\hsize
    \usebeamertemplate**{caption}\par
    \else
    \global \@minipagefalse
    \hb@xt@\hsize{\hfil\box\@tempboxa\hfil}%
    \fi
    \nobreak\vskip\belowcaptionskip\nobreak%
}
\def\listoffigureformat#1#2#3#4{%
    \makebox[2ex][r]{#1}%
    \hspace{1ex}%
    {\usebeamercolor[fg]{bibliography entry author} #2}%
    \ifthenelse{\equal{#4}{\empty}}{}{ -- #4}%
    \dotfill%
    \makebox[2ex][r]{#3}\par%
}
\def\listoffigures{%
    \setlength{\leftskip}{3ex}
    \setlength{\parindent}{-3ex}
    \@starttoc{lof}%
}
\def\listoftableformat#1#2#3{\makebox[2ex][r] 
{#1}\hspace{1ex}#2\dotfill\makebox[2ex][r]{#3}\par}
\def\listoftables{%
    \setlength{\leftskip}{3ex}
    \setlength{\parindent}{-3ex}
    \@starttoc{lot}%
}
\long\def\@caption#1[#2]#3{
    \par\nobreak
    \begingroup
    \@parboxrestore
    \if@minipage
    \@setminipage
    \fi
    \beamer@makecaption{#1}{\ignorespaces #3}{\ignorespaces #3} 
{\ignorespaces #2}\par\nobreak
    \endgroup}
\makeatother

\begin{document}

\begin{frame}{Frame}
\begin{figure}
\mbox{A}
\caption[citation]{The letter 'A'}
\end{figure}
\begin{itemize}
    \item<1-> an item
    \item<2-> another item
    \item<3-> a third item
\end{itemize}
\end{frame}
\begin{frame}{List of Figures}
\listoffigures
\end{frame}

\end{document}