[Tex/LaTex] Number of rows in loaded table

pgfplotspgfplotstable

Is it possible to determine the number of rows in a table read by pgfplotstableread{values.dat}\val ?

My setup is the following. I make experiments to see how a parameter affects a convergence curve. Results of such experiments look like

[results.dat]
n err_0 err_1 err_2 err_3
1024 0.1 0.2 0.15
2084 0.01 0.02 0.015
4096 0.001 0.002 0.0015

Parameters for each experiment is saved in a second table

[meta.dat]
0.5
2
3.7
11

Now I want to plot the results automatically (without knowing the number of experiments or the parameters)

\documentclass[tikz]{standalone}
\usepackage{pgfplots}
\usepackage{pgfplotstable}
\begin{document}
\pgfplotstableread{results.dat}\values
\pgfplotstableread{meta.dat}\meta
\def\N{3} %change to automatic here

\begin{tikzpicture}
\begin{loglogaxis}
\foreach \i in {0,...,\N}{
%use elements from meta table here instead of \i
\edef\theLegend{\noexpand\addlegendentry{Generalized \i}}
\addplot table[x=n,y=err_\i]{\values};
\theLegend
}   
\end{loglogaxis}
\end{tikzpicture}
\end{document}

The two points I have trouble with are marked with comments.

Best Answer

Using the pointers of percusse and the answer https://tex.stackexchange.com/a/36472/5737 I came to the following solution for my problem.

\documentclass[tikz]{standalone}
\usepackage{pgfplots}
\usepackage{pgfplotstable}
\begin{document}
\pgfplotstableread{results.dat}\values
\pgfplotstableread{meta.dat}\meta
%number of experiments
\pgfplotstablegetrowsof{\meta}
\pgfmathsetmacro{\N}{\pgfplotsretval-1}  

\begin{tikzpicture}
\begin{loglogaxis}
\foreach \i in {0,...,\N}{
%get parameter
\pgfplotstablegetelem{\i}{[index]0}\of{\meta} 
\let\param\pgfplotsretval
\edef\theLegend{\noexpand\addlegendentry{Generalized \param}}
\addplot table[x=n,y=err_\i]{\values};
\theLegend
}   
\end{loglogaxis}
\end{tikzpicture}
\end{document}
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