[Tex/LaTex] Tikz foreach inside matrix

foreachmatricestikz-pgf

Apparently this question has been asked a hundred times already. But I couldn't get it to work with any of the answers provided.

I want to have nested for loops inside a Tikz matrix. Something like:

\begin{tikzpicture}[>=latex]
  \tikzstyle{every node}=[minimum size=3mm]
  \tikzset{pre/.style={draw,fill=black}}
  \matrix[matrix of math nodes,%
      left delimiter = (,%
      right delimiter = )] {%
    \foreach \i in {0,..,10} {%
      \foreach \j in {0,1} {%
        \node[pre](pre\i\j){}; &
      }
      \\
    }
  }
\end{tikzpicture}

Thanks to this and a couple of other posts I know that this cannot work.

So, I tried to translate it accordingly. But I cannot even get it to work with a simple non-nested loop:

\begin{tikzpicture}[>=latex]
  \tikzstyle{every node}=[minimum size=3mm]
  \tikzset{pre/.style={draw,fill=black}}
  \let\mymatrixcontent\empty
  \foreach \i in {0,1,2,3,4} {%
    \expandafter\gappto\expandafter\mymatrixcontent\expandafter{\i \&}%
  }
  \expandafter\gappto\expandafter\mymatrixcontent\expandafter{\\}%

  \matrix[matrix of math nodes,%
      nodes = {pre},%
      left delimiter = (,%
      right delimiter = ),
      ampersand replacement=\&] {%
    \mymatrixcontent
  };
\end{tikzpicture}

Latex fails with the extremely helpful message

! Missing } inserted.
<inserted text> 
                }
l.345 \end{tikzpicture}

What am I doing wrong? Is there an easier way to accomplish this?

Cheers!

Best Answer

The nested version looks like:

\documentclass{article}
\usepackage{etoolbox}
\usepackage{tikz}
\usetikzlibrary{matrix}

\begin{document}
\let\mymatrixcontent\empty
\newcommand{\row}{%
  \foreach \j in {1,...,10}{
    \foreach \i in {1,2} {%
      \begingroup\edef\x{\endgroup
         \noexpand\gappto\noexpand\mymatrixcontent{ pre-\i-\j \&}}\x
      }%
    \gappto\mymatrixcontent{\\}%
  }
}
\row

\begin{tikzpicture}
\tikzset{every node/.style={minimum size=3mm},
  pre/.style={draw,fill=yellow}}

  \matrix (a) [ampersand replacement=\&,matrix of math nodes, nodes={pre}]{
    \mymatrixcontent
  };
\end{tikzpicture}

\end{document}

enter image description here

Related Solutions

[Tex/LaTex] Foreach inside a TikZ matrix

\foreach isn't expandable and the grouping is most likely causing some issues as well. I would recommend to use the loop outside the matrix and accumulate the rows in a macro which then only has to be expanded. The etoolbox package provides \gappto (global append to; \xappto would cause issues with fragile content) which can be used here. There is also \g@addto@macro provided by the LaTeX kernel, if you don't want to rely on e-TeX and don't mind to have to use \makeatletter/\makeatother.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{matrix}
\usepackage{etoolbox}

\begin{document}

\begin{tikzpicture}
    \let\mymatrixcontent\empty
    \foreach \c in {a,b,c}{%
        \expandafter\gappto\expandafter\mymatrixcontent\expandafter{\c\\}%
        % or
        %\xappto\mymatrixcontent{\expandonce{\c\\}}
    }
    \matrix [matrix of nodes] {
        \mymatrixcontent
    };
\end{tikzpicture}

\end{document}

[Tex/LaTex] Rotate a node but not its content: the case of the ellipse decoration

The source of the difficulty is that ellipses are constructed in a particular way in TikZ. They are paths that start from the x-axis and proceed counter-clockwise around their centre. The vast majority of the time, the exact parametrisation doesn't matter. You appear to have found the one situation where it does!

In the actual question, you only want to be able to mirror the ellipse, and so draw it starting from the negative x-axis (the title of the question suggests a more flexible approach). That's actually not too hard since we can exploit the symmetry of the ellipse. The key is to provide it with a negative x-radius, since then it will start from the negative x-axis (and proceed clockwise, but we could correct for that by negating the y-radius as well). To do this, we interrupt the call from the node shape to the drawing command and flip the sign of the x-radius. The simplest way to do this is to redefine the \pgfpathellipse macro to do the negation and then call the original macro. The following code does this.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{decorations,shapes,decorations.markings}
\makeatletter
\let\origpgfpathellipse=\pgfpathellipse
\def\revpgfpathellipse#1#2#3{%
  #2%
  \pgf@xa=-\pgf@x
  \origpgfpathellipse{#1}{\pgfqpoint{\pgf@xa}{0pt}}{#3}}
\makeatother

\tikzset{
  reversed ellipse/.style={
    ellipse,
    reverse the ellipse%
  },
  reverse the ellipse/.code={
    \let\pgfpathellipse=\revpgfpathellipse
  }
}
\begin{document}
\begin{tikzpicture}
\node[ellipse,
  draw,
  postaction={
    decorate,
    decoration={
      markings,
      mark=at position 1 with {
        \arrow[line width=5pt,blue]{>}
      }
    }
  }
] at (0,0) {hello world};

\node[reversed ellipse,
  draw,
  postaction={
    decorate,
    decoration={
      markings,
      mark=at position 1 with {
        \arrow[line width=5pt,blue]{>}
      }
    }
  }
] at (0,-2) {hello world};
\end{tikzpicture}

\end{document}

Here's the result:

rotated ellipse

(the arrow got clipped, but you can see where it lies)

Best Answer

Related Solutions

[Tex/LaTex] Foreach inside a TikZ matrix

[Tex/LaTex] Rotate a node but not its content: the case of the ellipse decoration

Related Question