TikZ: Using already defined \node label with decimal precision in \draw

Question

I have labelled all my nodes in my code and some have decimal numbers in their labels. I want to use these labels as arguments in the \draw command but I keep getting this error

! Missing \endcsname inserted.

Below is a minimum working example.

\documentclass[12pt,a4paper]{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
%Putting node and clipping them to their respective positions
\foreach \x in {1/2,1,10/3,37/3,15.5}
    \foreach \y in {1,1.25,1.5,3,3.5,,4.5}
    {
        \node [circle,draw=white,fill=white,inner sep=0pt,minimum size=1.5mm] (u\x\y) at (\x,\y)  {};
    }
%Drawing arrows
\foreach \y in {1.5,3.5}
    {
        \draw[semithick,->] (u1/2\y) -- (u1\number\numexpr\y-0.5\relax) ;
    }
\end{tikzpicture}
\end{document}

Answer 1

Just as one should not use x[2.5] in a C program, one should avoid using Tikz names with floating point numbers (converted to text). But one can obtain the desired effect using Tikz arrays (not to be confused with LaTeX arrays).

\documentclass[12pt,a4paper]{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
%Putting node and clipping them to their respective positions
\def\xval{{1/2,1,10/3,37/3,15.5}}
\def\yval{{1,1.25,1.5,3,3.5,4,4.5}}
\foreach \x in {0,1,2,3,4}
    \foreach \y in {0,1,2,3,4,5,6}
    {
        \node [circle,draw=white,fill=white,inner sep=0pt,minimum size=1.5mm] (u\x*\y) at (\xval[\x],\yval[\y])  {};
    }
%Drawing arrows
\foreach \y in {2,4}
    {
        \draw[semithick,->] (u1*\y) -- (u1*\number\numexpr\y-1\relax) ;
    }
\end{tikzpicture}
\end{document}