[Tex/LaTex] How to keep the same mark colour when using meta data for marker size

pgfplots

Probably an easy answer to this, but I can't get it to work, and I obviously don't understand the manual or the other answers given to similar questions here on tex.sx (see 1,2, and 3).

Basically I want to use the values of an additional column in a table to specify the size of the markers, but keeping the colour the same for each marker (e.g., a colour defined by \definecolor{name}{rgb}{x1,x2,x3}).

An MWE doing almost what I want; the size of the markers is controlled by the third column as desired, but obviously the colour as well. What do I need to change in order to keep the colour constant for all the markers?

\documentclass[tikz]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=newest}
\usetikzlibrary{plotmarks}
\usepackage{amsmath}
\usepackage{filecontents}

\begin{filecontents*}{temp.dat}
1   1   100
2   2   200
3   3   300
4   4   400
5   5   500
6   6   600
7   7   700
8   8   800
9   9   900
10  10  1000
\end{filecontents*}

\begin{document}
\begin{tikzpicture}

\begin{axis}[%
width=4.5in,
height=3.5in,
scale only axis,
xmin=0,
xmax=10,
ymin=0,
ymax=10,
axis x line*=bottom,
axis y line*=left
]
\addplot[%
scatter,
only marks,
mark=*,
color=blue,
visualization depends on={\thisrowno{2} \as \perpointmarksize},
scatter/@pre marker code/.append style={/tikz/mark size=\perpointmarksize/50}] plot table[row sep=crcr]{temp.dat};
\end{axis}
\end{tikzpicture}%
\end{document}

Best Answer

The most straightforward way of letting the scatter style only change the size but not the colour of the marks is to add

scatter/@pre marker code/.style={/tikz/mark size=\pgfplotspointmeta/50},
scatter/@post marker code/.style={}

to the \addplot options. Note the use of .style instead of .append style. What happens when you load the scatter style is that, among other things, installs its own @pre marker code stuff that deals with changing the colour. By using @pre marker code/.style, you can overwrite that code with your own. Note that you'll also need to clear the @post marker code using /.style={} because otherwise it would contain an unmatched \endscope.

To be able to use the \pgfplotspointmeta macro for scaling the data points instead of a macro defined using visualization depends on, you need to set point meta=explicit symbolic in the \addplot options. This tells PGFPlots to expect a meta value for every data point, instead of simply using the y value. The symbolic keyword specifies that the value shouldn't be parsed and shouldn't be converted to floating point format, which would throw the standard math parser off.

\documentclass[tikz, border=5mm]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=newest}
\usetikzlibrary{plotmarks}
\usepackage{amsmath}

\begin{filecontents*}{temp.dat}
1   1   100
2   2   200
3   3   300
4   4   400
5   5   500
6   6   600
7   7   700
8   8   800
9   9   900
10  10  1000
\end{filecontents*}

\begin{document}
\begin{tikzpicture}

\begin{axis}[%
    width=4.5in,
    height=3.5in,
    scale only axis,
    xmin=0,
    xmax=10,
    ymin=0,
    ymax=10,
    axis x line*=bottom,
    axis y line*=left
]
\addplot[%
    scatter=true,
    only marks,
    mark=*,
    color=blue,
    point meta=explicit symbolic,
    scatter/@pre marker code/.style={/tikz/mark size=\pgfplotspointmeta/50},
    scatter/@post marker code/.style={}
] table [meta index=2] {temp.dat};
\end{axis}
\end{tikzpicture}%
\end{document}
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