tikz foreeach list is empty?

Question

I' m trying to make an animation with the following code

\documentclass[presentation]{beamer}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\usepackage{graphicx}
\usepackage{tikz}
\begin{document}
\section{Bilder}
\begin{frame}
\begin{tikzpicture}
[pedestrian/.style={circle,draw=blue!50,fill=blue!20,thick},
transition/.style={rectangle,draw=black!50,fill=black!20,thick}]
\draw[step=1cm,gray,very thin]  (-6,0) grid (3,1) ;

\let\mylist\empty
\foreach \x[count=\i] in {1,...,5}{
\node<\i> [gray,above] at (-7,0.2) {$step=\i$};
\pgfmathtruncatemacro\y{6-\i}
\foreach \x in {1,...,\y}
\node<\i>  at  (-6.5+\x, 0.5) [pedestrian] {\tiny{\x,\i,\y|\mylist}};

\ifx\mylist\empty
\xdef\mylist{5};
\else
\foreach \z in \mylist{
\node<\i> at  (-2.5+\i , 0.5) [pedestrian] {\tiny{\z}};
 }    
\xdef\mylist{\y,\mylist};
\fi
}

\end{tikzpicture}
\end{frame}

\end{document}

Something is wrong with the variable z which is alway 5. I checked the values of mylist, which keeps growing, but still... z is always 5 (the last element of the list).

Here is the result that I was expecting: PDF-FILE

I got it by doing some stupid copy-paste

\documentclass[presentation]{beamer}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\usepackage{graphicx}
\usepackage{tikz}
\usepackage{pgffor}
\begin{document}
\section{Bilder}
\begin{frame}
\begin{tikzpicture}
[pedestrian/.style={circle,draw=blue!50,fill=blue!20,thick},
transition/.style={rectangle,draw=black!50,fill=black!20,thick}]
\draw[step=1cm,gray,very thin]  (-6,0) grid (3,1) ;

\uncover<1>{
\node [gray,above] at (-7,0.2) {$step=0$};
\foreach \x in {1,...,5}
\node  at  (-6.5+\x + 0, 0.5) [pedestrian] {\tiny{\x}};
}

\uncover<2>{
\node [gray,above] at (-7,0.2) {$i=5$};
\foreach \x in {1,...,4}
\node  at  (-6.5+\x + 0, 0.5) [pedestrian] {\tiny{\x}};

\node  at  (-6.5+6 + 0, 0.5) [pedestrian] {\tiny{5}};
}

\uncover<3>{
\node [gray,above] at (-7,0.2) {$i=4$};
\foreach \x in {1,...,3}
\node  at  (-6.5+\x + 0, 0.5) [pedestrian] {\tiny{\x}};

\foreach \x in {4,...,5}
\node  at  (-6.5+1 + \x, 0.5) [pedestrian] {\tiny{\x}};
}
\uncover<4>{
\node [gray,above] at (-7,0.2) {$i=3$};
\foreach \x in {1,...,2}
\node  at  (-6.5+\x + 0, 0.5) [pedestrian] {\tiny{\x}};

\foreach \x in {3,...,5}
\node  at  (-6.5+1 + \x, 0.5) [pedestrian] {\tiny{\x}};

}
\uncover<5>{
\node [gray,above] at (-7,0.2) {$i=2$};

\foreach \x in {2,...,5}
\node  at  (-6.5+1 + \x, 0.5) [pedestrian] {\tiny{\x}};

\node  at  (-6.5 + 1, 0.5) [pedestrian] {\tiny{1}};
}

\uncover<6>{
\node [gray,above] at (-7,0.2) {$i = 1$};

\foreach \x in {1,...,5}
\node  at  (-6.5+1 + \x, 0.5) [pedestrian] {\tiny{\x}};

}

\end{tikzpicture}
\end{frame}

\end{document}

Answer 1

You example works but you are hit by beamer syntax <i>

Consider the line change on your last foreach loop

\node[opacity=0.2] at  (-2.5+\i , 0.5) [pedestrian] {\tiny{\z}};% It was <i> HERE

Then we see that the loop is run correctly but because all have the same slide specification <i> they got overprinted by the last element which happens to be 5.

Now we can see that the content is there. You can either try to fix this or you can use a more compact version such as the following (which you can even further code golf it)

\documentclass[presentation]{beamer}
\usepackage{tikz}
\begin{document}
\section{Bilder}
\begin{frame}
\begin{tikzpicture}
[pedestrian/.style={circle,draw=blue!50,fill=blue!20,thick,font=\tiny},
transition/.style={rectangle,draw=black!50,fill=black!20,thick}]
\draw[step=1cm,gray,very thin]  (-6,0) grid (3,1) ;

\foreach \x[count=\xi] in {5,...,0}{
  \foreach \y[count=\yi from 0] in {1,...,5}{
    \ifnum\yi<\x\relax
      \node<\xi>[pedestrian]  at  (-6.5+\y, 0.5)  {\y};
    \else
      \node<\xi>[pedestrian]  at  (-6.5+\y+1, 0.5)  {\y};
    \fi
    }
}
\end{tikzpicture}
\end{frame}
\end{document}