TikZ Loop through array of arrays

Question

I would like to loop over an array and access each x- and y-coordinate separately, because I want to modify the coordinates before using them on a node.

Currently it is only working when inserting the coordinates directly in the foreach loop, but my second example using an array is not working.

\documentclass{minimal}
\usepackage{tikz}

\begin{document}
    \begin{tikzpicture}

         \def\myarr {
          (1.0, 1.1),
           (0.5, 1.5),
           (1.5, 2)
         }

        \foreach \x/\y in {1/3, 2/7, 3/8} {
            \node () at (\x,\y) {\x and \y};
        }

        % Not working
        %\foreach \x/\y in {\myarr} {
        %    \node () at (\x,\y) {mynode};
        %}

    \end{tikzpicture}
\end{document}

How can I use an array to achieve the same result?

Answer 1

You can loop over coordinates, i.e. \foreach \X in \myarr { \node () at \X {mynode}; } works in your example. If you want to read out the x and y coordinates, you may do

\documentclass{minimal}
\usepackage{tikz}
\def\GetX(#1,#2)#3{\def#3{#1}}
\def\GetY(#1,#2)#3{\def#3{#2}}
\begin{document}
    \begin{tikzpicture}

         \def\myarr {
          (1.0, 1.1),
           (0.5, 1.5),
           (1.5, 2)
         }

        \foreach \X in \myarr {
            \edef\temp{\noexpand\GetX\X\noexpand\myx
            \noexpand\GetY\X\noexpand\myy}
            \temp
            \node () at \X {\myx\ and \myy};
        }

    \end{tikzpicture}
\end{document}

Answer 2

This shows how \myarr is parsed. Actually, the first parenthesis are ignores, then the commas inside the parenthesis are ignored.

\documentclass{minimal}
\usepackage{tikz}

\begin{document}
   \def\myarr {{
          (1.0, 1.1),
           (0.5, 1.5),
           (1.5, 2)
         }}
  \verb|\myarr[0]| = \myarr[0] 

  \pgfmathparse{\myarr[0]}\pgfmathresult

  \pgfmathparse{\myarr[1]}\pgfmathresult

  \pgfmathparse{\myarr[2]}\pgfmathresult

  \pgfmathparse{\myarr[3]}\pgfmathresult
\end{document}

produces