Graphics, Figures & Tables ⇒ TikZ: How can I use a matrix to define matrix elements?

[topsquark]

This is a bit crazy. Here's my code:

Code: Select all

\usetikzlibrary{matrix}
\begin{tikzpicture}
     \def\entry{{{First,Second},{Third,Fourth}}}
     \matrix[matrix of nodes] {
          {\entry[0][0]} & {\entry[0][1]} \\
          {\entry[1][0]} & {\entry[1][1]} \\
     };
\end{tikzpicture}

I'm trying to get the output
First Second
Third Fourth

but it prints out the whole matrix entry then [0][1] at each box.

Bah! This is simple. What am I doing wrong?

Thanks!

-Dan

[Bartman]

Read section "94.2 Syntax for Mathematical Expressions: Operators" on how to evaluate the array-like structure of your \entry command's definition.

Code: Select all

\documentclass[tikz]{standalone}
\usetikzlibrary{matrix}

\begin{document}
\begin{tikzpicture}
  \newcommand{\print}[1]{\pgfmathparse{#1}\pgfmathresult}
  \newcommand{\entry}{{{"First","Second"},{"Third","Fourth"}}}
  \matrix[
    matrix of nodes,
    execute at begin cell=\print
  ] {
    {\entry[0][0]} & {\entry[0][1]} \\
    {\entry[1][0]} & {\entry[1][1]} \\
  };
\end{tikzpicture}
\end{document}

[topsquark]

Read section "94.2 Syntax for Mathematical Expressions: Operators" on how to evaluate the array-like structure of your \entry command's definition.

Code: Select all

\documentclass[tikz]{standalone}
\usetikzlibrary{matrix}

\begin{document}
\begin{tikzpicture}
  \newcommand{\print}[1]{\pgfmathparse{#1}\pgfmathresult}
  \newcommand{\entry}{{{"First","Second"},{"Third","Fourth"}}}
  \matrix[
    matrix of nodes,
    execute at begin cell=\print
  ] {
    {\entry[0][0]} & {\entry[0][1]} \\
    {\entry[1][0]} & {\entry[1][1]} \\
  };
\end{tikzpicture}
\end{document}

Thank you! A bit less obvious than I thought it would be, but obvious enough once I saw what the problem was.

Yes, I finally figured out today that the contents of {..} is considered text, no matter that a variable {\x} might look like a number. I haven't really spent much time with the pgf codes. My loss, apparently.

I have two more questions if you don't mind.
1) I can make this work with \def\entry{{{..}}}. Is there an advantage in using \newcommand?

2) "execute at begin cell" is a neat trick. I'll have to remember that. I would like you to check my understanding of how that works. It tells the matrix operation to run \print on, say, the \entry[0][0] element and returns the number to the 0,0 position in the matrix, inside the { }, where it can be processed properly. This avoids the problem of trying to do something like {\print(\entry[0][0])}, which just repeats my initial mistake and shouldn't work. (I apologize for the likely bad terminology, clearly I'm a noob programmer.)

Thanks for the help!

-Dan