Save TikZ plot points calculated with PGF math library to .table file?

Question

Is it possible to let TikZ save and in subsequent compilation runs use the plot points generated with the PGF math library?

A (simple) example of such a function plotted that way is:

\begin{tikzpicture}
  \draw plot (\x,{sin(2*pi*\x r)});
\end{tikzpicture}

Here, the PGF math library is used to calculate sin(2*pi*\x r). For complex expressions, this is quite time-intensive. I assume this time could be saved if the plot points were available as is the case when using a gnuplot ‘function’ plot. Then (if the plot is given an id) the plot points generated by gnuplot are saved to a .table file, so that they need not be regenerated unless the plot parameters have changed.

Answer 1

You can use \pgfplotstablenew command from pgfplotstable (which comes with pgfplots) to create a file with your plot points and some conditional to create it when you want. Next example creates the file when doesn't exist.

\documentclass[border=2mm]{standalone}
\usepackage{pgfplots, pgfplotstable}

\begin{document}

\IfFileExists{myplot.dat}{}{
\pgfplotstablenew[
    create on use/plot1/.style={
        create col/expr={sin (2*pi*\pgfplotstablerow)}
    },
    columns={plot1}
]
{700}
\loadedtable
\pgfplotstablesave{\loadedtable}{myplot.dat}
}


  \begin{tikzpicture}
   \begin{axis}[
        line join=bevel,
        no markers,
        table/x expr={\coordindex},
        xmin=0,
        enlarge x limits=false,
        ymin=-1.5,
        ymax=1.5,
    ]
   \addplot[red] table [y expr={\thisrow{plot1}}] {myplot.dat};
\end{axis}

\end{tikzpicture}

\end{document}