Pgfplots – How to Get Max/Min Value in a Table Column with Pgfplot?

pgfplots

I'd like to get the max/min value from a specific column table via function \findmax and \findmin in order to use it in ymin and ymax.
I really dont get how \pgfplotstablesort function works. What would be perfect is to call \findmax{YAmax,YA,YAmin} and get back the maximum value of those 3 columns.

\documentclass{standalone}
\usepackage{pgfplots}
\usepackage{pgfplotstable}
\usepackage{filecontents}

\newcommand{\findmax}[1]{
    \pgfplotstablesort[sort key={#1},sort cmp={float >}]{\sorted}{data.dat}%
    \pgfplotstablegetelem{0}{1}\of{\sorted}%
    \let\ymax=\pgfplotsretval%
}

\begin{filecontents}{data.dat}
X   YA  YAmin   YAmax   YB  YBmin   YBmax
1   5   4   6   6   5   7
2   3   2   5   7   5   9
3   6   1   9   9   7   13
4   4   2   6   6   1   11
5   0   -1  3   3   0   5
6   1   -3  6   1   -1  2
\end{filecontents}



\begin{document}


\pgfplotsset{width=3cm,scale only axis}

\begin{tikzpicture}


%\findmax{YAmax,YA,YAmin}
%\findmin{YAmin,YA,YAmin}
\begin{axis}[at={(0,0)},title=YA]%,ymin=\ymin,ymax=\ymax]
\addplot [very thick,smooth,red,solid]  table [x=X, y=YA]   {data.dat}; 
\addplot [very thick,smooth,red,dotted]  table [x=X, y=YAmin]   {data.dat}; 
\addplot [very thick,smooth,red,dotted]  table [x=X, y=YAmax]   {data.dat}; 
\end{axis}

%\findmax{YBmax,YB,YBmin}
%\findmin{YBmax,YB,YBmin}
\begin{axis}[at={(4cm,0)},title=YB]%,ymin=\ymin,ymax=\ymax]
\addplot [very thick,smooth,red,solid]  table [x=X, y=YB]   {data.dat}; 
\addplot [very thick,smooth,red,dotted]  table [x=X, y=YBmin]   {data.dat}; 
\addplot [very thick,smooth,red,dotted]  table [x=X, y=YBmax]   {data.dat}; 
\end{axis}

\end{tikzpicture}
\end{document}

Best Answer

Finally done it.

Just created a function that finds the extrema of a chosen column of the external table.

\newcommand{\findmax}[1]{
  % Starting value for max : 0
  \pgfmathtruncatemacro{\mymax}{0}

  % Parsing each element of the first column
  \pgfplotsinvokeforeach {0,...,5}{
    \pgfplotstablegetelem{##1}{#1}\of{\mytable}
    \ifthenelse{ \pgfplotsretval >\mymax  }
    {\pgfmathtruncatemacro{\mymax}{\pgfplotsretval}} % valid
    {}  %invalid
  }
  \let\ymax=\mymax%
}
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