pgfplots: putting marker labels outside of the plot

Question

the following code:

\documentclass{article}

\usepackage[english]{babel}

\usepackage{pgfplots}      

\usepackage{tikz}
\usepgfplotslibrary{groupplots}

\begin{document}

\begin{figure}
\begin{tikzpicture}
\pgfplotsset{width=7cm}
\pgfplotsset{every axis title/.style={at={(0.5,0)},below,yshift=-24pt}}
\pgfplotsset{every axis grid/.append style={very thin,dashed,gray}}

\begin{groupplot}[
group style={
xlabels at = edge bottom,
ylabels at = edge left},
width=0.67\linewidth,
height=0.67\linewidth,
xlabel={Original},
every axis x label/.style=
{at={(ticklabel cs:0.5)},anchor=near ticklabel, font=\scriptsize},
ylabel={DiSL-based},
every axis y label/.style=
{at={(ticklabel cs:0.5)},rotate=90,anchor=near ticklabel, font=\scriptsize},
xtick={500,1500,2500},
xticklabel={\axisdefaultticklabel },
ytick={500,1500,2500},
yticklabel={\axisdefaultticklabel },
extra x tick style={grid=major},
extra y tick style={grid=major},
axis equal,
ticklabel style={font=\scriptsize},
cycle list={
{black,fill=lightgray},
},
nodes near coords,
legend entries = {$ASM$, $AspectJ$, $other$,$geo. mean$},
legend columns=-1,
legend style={font=\scriptsize},
legend style={draw=none},
legend style={at={(0.75,1.18)}}
]
\nextgroupplot[title={},xmin=0,ymin=0,xmax=2500,ymax=2500]
\addplot+[ mark=*,only marks, point meta=explicit symbolic, font=\scriptsize]      coordinates {
(650,70) [jcarder]% jcarder 
(470, 105) [jp2]% jp2
(1306, 37) [jrat]% jrat
(2489 , 280)[emma] % emma 
(1048,788) [cobertura]% cobertura
};
\nextgroupplot[title={},xmin=0,ymin=0,xmax=2500,ymax=2500]
\addplot+[mark=square*,fill=lightgray,only marks, point meta=explicit symbolic,    font=\scriptsize] coordinates {
(100, 225) [senseo]% senseo
(120, 124) [racer]% racer
};
\draw[/pgfplots/every axis grid] (axis cs:0,0) -- (axis cs:2500,2500);
\end{groupplot}
\end{tikzpicture}

gives me a plot with very dense marker labels that are hard to read. Unfortunately I can't post images here, but my question is there a way to put the marker labels (racer, senseo, jp2) outside of the plot and direct to the markers with arrow?

Answer 1

Yes, you can. An idea would be to let pgfplots generate labelled coordinates automatically for you - and then you can add custom nodes, placed wherever you would like to have them, and connect to the labelled nodes.

I modified your example accordingly:

\documentclass{article}

\usepackage[english]{babel}

\usepackage{pgfplots}      

\usepackage{tikz}

\begin{document}

\begin{tikzpicture}
\pgfplotsset{width=7cm}
\pgfplotsset{every axis title/.style={at={(0.5,0)},below,yshift=-24pt}}
\pgfplotsset{every axis grid/.append style={very thin,dashed,gray}}

\begin{axis}[
title={},xmin=0,ymin=0,xmax=2500,ymax=2500,% ---- CF
width=0.67\linewidth,
height=0.67\linewidth,
xlabel={Original},
every axis x label/.style=
{at={(ticklabel cs:0.5)},anchor=near ticklabel, font=\scriptsize},
ylabel={DiSL-based},
every axis y label/.style=
{at={(ticklabel cs:0.5)},rotate=90,anchor=near ticklabel, font=\scriptsize},
xtick={500,1500,2500},
xticklabel={\axisdefaultticklabel },
ytick={500,1500,2500},
yticklabel={\axisdefaultticklabel },
extra x tick style={grid=major},
extra y tick style={grid=major},
axis equal,
ticklabel style={font=\scriptsize},
cycle list={
{black,fill=lightgray},
},
nodes near coords=,% ---------- CF
every node near coord/.style={anchor=center,name=N-\pgfplotspointmeta},% ------- CF
legend entries = {$ASM$, $AspectJ$, $other$,$geo. mean$},
legend columns=-1,
legend style={font=\scriptsize},
legend style={draw=none},
legend style={at={(0.75,1.18)}}
]
\addplot+[ mark=*,only marks, point meta=explicit symbolic, font=\scriptsize]      coordinates {
(650,70) [jcarder]% jcarder 
(470, 105) [jp2]% jp2
(1306, 37) [jrat]% jrat
(2489 , 280)[emma] % emma 
(1048,788) [cobertura]% cobertura
};
\addplot+[mark=square*,fill=lightgray,only marks, point meta=explicit symbolic,    font=\scriptsize] coordinates {
(100, 225) [senseo]% senseo
(120, 124) [racer]% racer
};
\draw[/pgfplots/every axis grid] (axis cs:0,0) -- (axis cs:2500,2500);
\end{axis}

\draw
   (current axis.north east) 
     ++ (20pt,0pt) 
     node {JCarder} 
   edge (N-jcarder);

\draw
   (current axis.north east) 
     ++ (20pt,-20pt) 
     node {Senseo} 
   edge (N-senseo);

\end{tikzpicture}

\end{document}

Note that I eliminated the group plot - it was unnecessary altogether (since pgfplots adds plots to the current axis anyway).

The code consists in the following changes:

• use nodes near coords={}. The empty value tells pgfplots to not write anything into the node as such.

• provide a style for every node near coord which assigns a name to each of these nodes. The name is N-\pgfplotspointmeta where \pgfplotspointmeta expands to your symbolic names. In other words: the names are like N-jcarder etc.

• add custom \draw instructions which place text nodes somewhere and use TikZ's edge path to connect the new text nodes with N-jcarder etc. I suppose that you may want to place these labels very individually; my choice is merely some starting point.