# How to plot the first n rows of a table using pgfplots?

When using pgfplots, is there a way to plot only the first n rows of a given table ?

Considering the following MWE file:

\documentclass[tikz]{standalone}

\usepackage{tikz}
\usepackage{pgfplots}
\usepackage{amsmath}

\begin{document}

\begin{tikzpicture}
\begin{axis}[%
width=16cm,height=8cm,
view={-45}{65},
scale only axis,
xmin=200,xmax=500,
xlabel={data1},
ymin=0,ymax=100,
ylabel={data2},
zmin=0,zmax=1,
zlabel={data3},
]
thick,smooth,
color= darkgray,
solid]
table[row sep=crcr] {
250 0 0\\
250 25 0.2\\
250 50 0.3\\
250 75 0.2\\
250 100 0\\
};

thick,smooth,
color= darkgray,
solid]
table[row sep=crcr] {
450 0 0.5\\
450 25 0.1\\
450 50 0\\
450 75 0.1\\
450 100 0.5\\
};
\end{axis}
\end{tikzpicture}%
\end{document}


How can I plot only the first n=4 rows of each table and ask pgfplots to stop reading the table once this row is reached ?

Of course, for the above example, this seems useless, but when huge data tables are used, this could be extremely usefull, in particular to use the same data and focus on different parts of the table in different figures.

-
Just a hint for the next time: try to make your example smaller by reducing it to the essentials that are relevant to the problem you want to solve. For example, all those styles and fancy 3d plots are not really necessary. That makes it easier for people to help you. :-) – Fritz Sep 3 '14 at 21:30
Related: Remove rows in a \addplot table command (for plotting only the last n rows of a table). – Jake Sep 3 '14 at 22:52
@Fritz Thanks for the comment and thanks for the answer ! – Nicolas Sep 4 '14 at 19:52

Here is a style that allows you to select the rows N through M (inclusive, starting at 0) by specifying select coords between index={N}{M}. To select the first N points, you would specify select coords between index={0}{N-1}.

It is based on the explanation of the filter point style in the pgfplots manual. There is also an oppposite style that is already part of pgfplots: skip coords between index={N}{M} discards all points that are inside the range N to M.

The code below results in this cropped parabola:

\documentclass[tikz]{standalone}
\usepackage{pgfplots}

% Style to select only points from #1 to #2 (inclusive)
\pgfplotsset{select coords between index/.style 2 args={
x filter/.code={
\ifnum\coordindex<#1\def\pgfmathresult{}\fi
\ifnum\coordindex>#2\def\pgfmathresult{}\fi
}
}}

\usepackage{filecontents}
\begin{filecontents}{data.txt}
X    Y
-3    9      %  0 left out
-2    4      %  1 plotted
-1    1      %  2 plotted
-0.5  0.25   %  3 plotted
0    0      %  4 plotted
0.5  0.25   %  5 plotted
1    1      %  6 left out
2    4      %  7 left out
3    9      %  8 left out
\end{filecontents}

\begin{document}
\begin{tikzpicture}
\begin{axis}
\addplot [select coords between index={1}{5}] table {data.txt};
\end{axis}
\end{tikzpicture}
\end{document}

-
I am using this on a table with 250+ rows and it seems somewhat inefficient. Main thing is, it works! Is there a more efficient way? – SpmP Feb 8 '15 at 9:30
Is it much slower than plotting the whole table without filtering? I'd guess it should be about the same speed because PGFplots still needs to parse all coordinates. Maybe it could be made faster by first filtering the the values into a smaller temporary table and then plot that with PGFplots. However, you should probably post a separate question about that, because here it will be difficult to find. – Fritz Feb 9 '15 at 8:21
It did seem very slow as the throwing out coordinates blah was not quick in succession. The table is very big tho. Splitting into smaller sub-tables may be the way to go. Will ask a question on it. – SpmP Feb 12 '15 at 0:05