TikZ: How to use draw options only for coordinates which exists / foreach-problem

Question

I have some coordinates (say A, B, C).

Now I make sth. like this: \foreach \P in {A,B,C} \draw[fill=pink] (\P) circle[radius=2.5pt];

If I would have said \foreach \P in {A,B,C,X} \draw[fill=pink] (\P) circle[radius=2.5pt];

I would have got the error No shape named 'X' is known.

So my question is: How could I have sth. like the symbolic code

\ifcoordinateexist 
\draw[fill=pink]  (\P) circle[radius=2.5pt];
\else % nothing
\fi

I there a simple solution, maybe with TikZ-tools?

\documentclass[border=2mm, tikz]{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}[]
\coordinatelabel=A at (0,0);
\coordinatelabel=B at (2,3);
\coordinatelabel=C at (1,1);
% Will work:
\foreach \P in {A,B,C} \draw[fill=pink]  (\P) circle[radius=2.5pt];
%% Will not work:
%\foreach \P in {A,B,C,X} \draw[fill=pink]  (\P) circle[radius=2.5pt]; 
% ---------> No shape named `X' is known.
\end{tikzpicture}
\end{document}

score 4 · Answer 1 · edited Dec 20 '20 at 22:34

4

I found a solution here: https://tex.stackexchange.com/a/85531/46023

\documentclass[border=2mm, tikz]{standalone}
\usepackage{tikz}
\begin{document}
\makeatletter
\long\def\ifcoorddefined#1#2#3{%
    @ifundefined{pgf@sh@ns@#1}{#3}{#2}%
}
\makeatother
\begin{tikzpicture}[]
\coordinatelabel=A at (0,0);
\coordinatelabel=B at (2,3);
\coordinatelabel=C at (1,1);
\foreach \P in {A,B,C, X, Y, L, M}{
  \ifcoorddefined{\P}{  \draw[fill=pink] (\P) circle[radius=2pt];  }{}
}
\end{tikzpicture}
\end{document}

edited Dec 20 '20 at 22:34

muzimuzhi Z

26,474

answered Dec 16 '20 at 12:09

cis

8,073
1
16
45

1

+1 some comments: i) coordinate is a kind of specialized nodes, so naming the \ifXXX with \ifNodeDefined is better. ii) tikz nodes are defined globally (also mentioned in Martin Scharrer's original answer), so if there is a node X defined in previous tikzpicture(s), then this test would fail. – muzimuzhi Z Dec 16 '20 at 14:45
Ok, thx. ..... ;) – cis Dec 17 '20 at 19:10
@ muzimuzhi Z If you want, you could create an else-function and post it as an answer. That could be interesting. – cis Dec 19 '20 at 11:04
I'm wondering how to assign a distinct count to every tikzpicture which be used to assign a distinct internal macro to every node. This will take some time since I'm not familiar with the node implementations yet. – muzimuzhi Z Dec 19 '20 at 16:47
I added a missing empty argument to use of \ifcoorddefined. – muzimuzhi Z Dec 20 '20 at 22:34

score 1 · Accepted Answer · answered Dec 20 '20 at 22:32

As pointed in my previous comment,

tikz nodes are defined globally (also mentioned in Martin Scharrer's original answer), so if there is a node X defined in previous tikzpicture(s), then this test (the \ifcoorddefined in this answer) would fail.

Here is an enhanced tester \ifNodeDefined{<node name>}{<true>}{<false>} which can test whether the given node is defined in the current pgfpicure, an environment internally used by tikzpicture.

\documentclass{article}
\usepackage{tikz}
\makeatletter
\long\def\ifcoorddefined#1#2#3{%
    @ifundefined{pgf@sh@ns@#1}{#3}{#2}%
}
\def\ifNodeDefined#1{%
    @ifundefined{pgf@sh@ns@#1}{@secondoftwo}{%
      \expandafter\ifx\csname pgf@sh@pi@#1\endcsname\pgfpictureid
        \expandafter@firstoftwo
      \else
        \expandafter@secondoftwo
      \fi}%
}
\makeatother
\begin{document}
\begin{tikzpicture}
  \coordinate[label=X] (X) at (1,0);
  \coordinate[label=Y] (Y) at (0,1);
\end{tikzpicture}
\qquad
\begin{tikzpicture}[baseline=0pt]
  \coordinate[label=A] (A) at (0,0);
  \coordinate[label=B] (B) at (2,3);
  \coordinate[label=C] (C) at (1,1);
\foreach \P in {A,B,C, X, Y, L, M}{
    \ifcoorddefined{\P}
      {\draw[fill=pink] (\P) circle[radius=2pt];}
      {}
  }
  \node[anchor=north] at (1,-.5) {old tester};
\end{tikzpicture}
\qquad
\begin{tikzpicture}[baseline=0pt]
  \coordinate[label=A] (A) at (0,0);
  \coordinate[label=B] (B) at (2,3);
  \coordinate[label=C] (C) at (1,1);
\foreach \P in {A,B,C, X, Y, L, M}{
    \ifNodeDefined{\P}
      {\draw[fill=pink] (\P) circle[radius=2pt];}
      {}
  }
  \node[anchor=north] at (1,-.5) {new tester};
\end{tikzpicture}
\end{document}

TikZ: How to use draw options only for coordinates which exists / foreach-problem

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