# Use first row of a table as legend entry in pgfplot graph?

I'm using pgfplots extensively and I'd like to avoid having to write legends every time, since all the text files I want to plot have explicit headers.

As a comparison, \pgfplotstabletypeset makes a nice table instantly with my data, and I'm looking for a similar way to get graphs in an easier way than having to specify each column, legend, etc....

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## 2 Answers

You can access the column names of a PGFplots table through the macro \pgfplotstablegetcolumnnamebyindex{<index>}\of{<table macro>}\to{<macro>}. You can use this while looping through the columns of a table using \pgfplotsinvokeforeach{<list>}{<commands>} to add the column names as legend entries.

I've written a \plotfile macro that takes a filename as argument and then plots all columns starting from the second column against the first column:

\documentclass{article}
\usepackage{pgfplots}
\usepackage{filecontents}

\begin{filecontents}{testdata.dat}
Time Distance Velocity Something
0 0 1 0.2
1 1 1 0.3
1.999 1.999 1 0.4
2 2 0 0.4
3 2 0 0.5
\end{filecontents}

\newcommand{\plotfile}[1]{
\pgfplotstableread{testdata.dat}{\table}
\pgfplotstablegetcolsof{testdata.dat}
\pgfmathtruncatemacro\numberofcols{\pgfplotsretval-1}
\pgfplotsinvokeforeach{1,...,\numberofcols}{
\pgfplotstablegetcolumnnamebyindex{##1}\of{\table}\to{\colname}
\addplot table [y index=##1] {testdata.dat};
\addlegendentryexpanded{\colname}
}
}

\begin{document}
\begin{tikzpicture}
\begin{axis}[legend pos=north west]
\plotfile{testdata.dat}
\end{axis}
\end{tikzpicture}
\end{document}


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awesome thanks a lot. – ben paillard Jul 27 '11 at 22:25
@Jake, i tried this solution where instead of defining \newcommand{\plotfile}[1], i simply apply it below \begin{axis} and it didn't work. I am interesting to know why... What is the reason? – Eagle Feb 16 '12 at 9:55

I used the following to read a file, plot some columns and add legend entries, this worked fine:

\begin{figure}[!t]%
\centering
\begin{tikzpicture}
\begin{axis}[
width=\columnwidth, height=0.7\columnwidth,
xlabel={Frequency (GHz)}, ylabel={Image rejection (dB)}]
\pgfplotstableread{data/Simulation.txt}\SimIR
\foreach \n in {3,4,...,6} {
\addplot table[x=IF,y index=\n]{\SimIR};
\pgfplotstablegetcolumnnamebyindex{\n}\of{\SimIR}\to{\colname}
\addlegendentryexpanded{\colname}
}%
\end{axis}
\end{tikzpicture}
\caption{Image rejection versus frequency.}%
\label{fig:IR}%
\end{figure}

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If I understand correctly, the main differences between this and my answer are the use of \foreach instead of \pgfplotsforeachungrouped and the hard-coding of the columns to be plotted? – Jake Jan 25 '14 at 15:49