pgfplots - A TeX package to draw normal and/or logarithmic plots directly in TeX in two and three dimensions with a user-friendly interface and pgfplotstable - a TeX package to round and format numerical tables. Examples in manuals and/or on web site.
When table is read from file and /pgf/number format/read comma as period is turned on, commands \thisrow and \thisrowno used in y expr=<math expr> will throw errors.
I find only the math function form thisrow("y") is usable.
\begin{filecontents}[noheader,force]{data-comma.txt}
x y
1 1,0
2 2,0
3 5,0
\end{filecontents}
\begin{filecontents}[noheader,force]{data-period.txt}
x y
1 1.0
2 2.0
3 5.0
\end{filecontents}
\documentclass{article}
\usepackage{pgfplots}
\pgfplotsset{compat=1.18}
\begin{document}
\begin{tikzpicture}
\begin{axis}
\addplot table[
/pgf/number format/read comma as period,
y expr={thisrow("y")+1},
% y expr={\thisrow{y}+1}, % not working
% y expr={\thisrowno{1}+1}, % not working
] {data-comma.txt};
\addplot table[y expr=\thisrow{y}+2] {data-period.txt};
\end{axis}
\end{tikzpicture}
\end{document}
From https://tex.stackexchange.com/q/647366
When table is read from file and
/pgf/number format/read comma as period
is turned on, commands\thisrow
and\thisrowno
used iny expr=<math expr>
will throw errors.I find only the math function form
thisrow("y")
is usable.