Rolling bullet points in beamer

Question

Often when I use beamer for slides I use an itemize environment with \pause to show off one bullet point at a time. Also, often all the points I want to show on a single slide does not fit and I need to start a new slide with a couple of more points.

What I would like is instead an itemize-like environment that would give me (when the points do not fit on a single slide) rolling bullet points, something similar to what the following code does:

\documentclass{beamer}
\begin{document}
    \begin{frame}
        \begin{itemize}
            \only<-5>{\item one}
            \only<2-6>{\item two}
            \only<3-7>{\item three}
            \only<4-8>{\item four}
            \only<5-9>{\item five}
            \only<6-10>{\item six}
            \only<7-11>{\item seven}
            \only<8-12>{\item eight}
            \only<9->{\item nine}
            \only<10->{\item ten}
            \only<11->{\item eleven}
            \only<12->{\item twelve}
        \end{itemize}
    \end{frame}
\end{document}

However I don't want to keep track of how many slides I'm using.

Is there such an environment out there somewhere?

Also, some sort of animated rolling would be excellent, but that might be to ask for to much.

Answer 1

This is built into beamer:

\documentclass{beamer}
\begin{document}
\begin{frame}
    \begin{itemize}[<only@+-+(4)>]
        \item one
        \item two
        \item three
        \item four
        \item five
        \item six
        \item seven
        \item eight
        \item nine
        \item ten
    \end{itemize}
\end{frame}
\end{document}

The overlay specification +-+(4) means the same thing as (n+1)-(n+5), where n is the current slide count. The only@ action wraps the item in an \only<...>. Putting the specification as an argument to the itemize environment makes it the default for each item.

If you want to specify item text in a \foreach loop you can explicitly call \only before each item:

\documentclass{beamer}
\usepackage{pgffor}
\begin{document}
\begin{frame}
    \begin{itemize}
        \foreach \x in {a,b,...,z} {%
            \only<+-+(4)>{\item \x}
        }
    \end{itemize}
\end{frame}
\end{document}

See sections 9.6.3 (Action Specifications) and 9.6.4 (Incremental Specifications) of the beamer (v3.22) manual. Also this answer of mine.

Answer 2

Here's a version, with a rather weird problem and therefore a limitation. It defines a new counter iii and a new \myitem command. If you use such itemize environments on more than one slide, then the counter has to be reset. Otherwise, if for example you had 10 points on the first slide, it would start at slide 11 on the next slide. So I used etoolbox's \AtBeginEnvironment to reset the iii counter. This however means that you can only use one such itemize list per frame as otherwise you'll scroll through both of them at the same time. I tried to improve this by reseting the iii counter at the begin of each frame. But if I don't have the line \AtBeginEnvironment{itemize}{\setcounter{iii}{0}} I get a large pile of errors ("perhaps a missing item"), so for the moment this is limited to one scrolling itemize per frame. Also, as there's no look ahead mechanism, it won't stop when the last 5 items are displayed, but only when the last one is present.

Code

\documentclass{beamer}
\usetheme{Darmstadt}
\usepackage{tikz}
\usepackage{etoolbox}

\newcounter{iii}

\AtBeginEnvironment{itemize}{\setcounter{iii}{0}}

\newcommand{\myitem}[2][$\bullet$]
{ \stepcounter{iii}
    \pgfmathtruncatemacro{\endslide}{\theiii+4}
    \only<\theiii-\endslide>{\item[#1] #2}
}

\begin{document}

\begin{frame}[t]
    \begin{itemize}
        \myitem{a \theiii}
        \myitem{b \theiii}
        \myitem{c \theiii}
        \myitem{d \theiii}
        \myitem{e \theiii}
        \myitem{f \theiii}
        \myitem{g \theiii}
        \myitem{h \theiii}
        \myitem{i \theiii}
        \myitem{j \theiii}
        \myitem{k \theiii}
        \myitem{l \theiii}
        \myitem{m \theiii}
        \myitem{n \theiii}
        \myitem{o \theiii}
        \myitem{p \theiii}
        \myitem{q \theiii}
        \myitem{r \theiii}
        \myitem{s \theiii}
        \myitem{t \theiii}
        \myitem{u \theiii}
        \myitem{v \theiii}
        \myitem{w \theiii}
        \myitem{x \theiii}
        \myitem{y \theiii}
        \myitem{z \theiii}
    \end{itemize}
\end{frame}

\end{document}

Result

Answer 3

For reference as an extension to @Matthew Leingang's excellent answer. here is how you hardcode the beginning and end to avoid even having the list display less than 4 items.

\documentclass{beamer}
\usepackage{pgffor}
\begin{document}
\begin{frame}
    \begin{itemize}
        \only<-1>{\item 1}
        \only<-2>{\item 2}
        \only<-3>{\item 3}
        \only<+-+(3)>{\item 5}
        \only<+-+(3)>{\item 6}
        \only<+-+(3)>{\item 7}
        \only<+-+(3)>{\item 8}
        \only<+-+(3)>{\item 9}
        \only<+-+(3)>{\item 10}
        \only<+-+(3)>{\item 11}
        \only<+-+(3)>{\item 12}
        \only<+-+(3)>{\item 13}
        \only<+->{\item 14}
        \only<+->{\item 15}
        \only<+->{\item 16}
        \only<+->{\item 17}
    \end{itemize}
\end{frame}
\end{document}