How to use variables in node keys in TikZ

Question

I have used variable \x while drawing nodes using TiKZ. The drawing part works well without any problems. I have also added keys to the nodes so that they can be linked later. I am facing a curious problem. The node key works if the \x is a whole number, but doesn't work if it is a decimal.

For example, in the code below, I am using the key as \x g2y.

\fill[fill=yellow]
\foreach \x in {2.5,7,11.5} 
{ (\x,10) circle(.45) node(\x g2y) {}};

Now when I try to use the keys from here, only the key with \x value 7 works. For other values of \x like 2.5 and 11.5 it gives an error:

ERROR: Package pgf Error: No shape named 2 is known.

Somehow, the entire decimal value of the number is not being passed to the key, only the whole number before the decimal. How can this be resolved?

MWE is appended below:

\documentclass{article}
\usepackage{tikz}
\begin{document}

\begin{tikzpicture}[scale=.5]

\fill (9,13.5)[fill=yellow] circle(.5) node (g1){};

 \fill[fill=yellow]
 \foreach \x in {2.5,7,11.5} 
 { (\x,10) circle(.45) node(\x g2y) {}};
% works here with only 7
\draw [red!50,thick]\foreach \x in {7}
 {(g1)--(\x g2y)};

% doesn't works here with 2.5 and 11.5
% \draw [red!50,thick]\foreach \x in {2.5,7,11.5} 
% {(g1)--(\x g2y)};

\end{tikzpicture}
\end{document}

Answer 1

The problem is that TikZ uses . to access an anchor of a node, for example a.west. So when you have a node called 2.5g2y, and use that in a \draw, TikZ thinks that is a node called 2, and the anchor would be 5g2y.

I don't know if it's possible to use periods in node names, but a workaround is to add a count to your loop, and use that value instead.

Unrelated comment: in general the minimal class should be avoided, see Why should the minimal class be avoided?

\documentclass{article}
\usepackage{tikz}
\begin{document}

\begin{tikzpicture}[scale=.5]

\fill (9,13.5)[fill=yellow] circle(.5) node (g1){};

 \fill[fill=yellow]
 \foreach [count=\i] \x in {2.5,7,11.5} 
 { (\x,10) circle(.45) node(\i g2y) {}};

\draw [red!50,thick]\foreach \x in {1,2,3}
 {(g1)--(\x g2y)};

\end{tikzpicture}
\end{document}