pgfplots dollar sign in node, adjust space between bars

Question

I'd like to format the nodes in this bar chart with $ signs (e.g $275). (The sets of bars could also be closer together; perhaps that should be another question.)

The answer is probably out there somewhere but my searches haven't found it.

Here's my MWE:

%http://tex.stackexchange.com/questions/88892/pgfplots-bar-plot-spacing-inbetween-bars
%http://tex.stackexchange.com/questions/113241/pgfplots-grouped-bar-chart-from-file
%http://tex.stackexchange.com/questions/35872/multiline-coords

\documentclass{standalone}
\usepackage{tikz,pgfplots}
\usepackage{pgfplotstable}

\usetikzlibrary{calc,decorations.pathmorphing}

%deal with warning message in log
\pgfplotsset{compat=1.8}

\usepackage{helvet}
\usepackage[eulergreek]{sansmath}

\begin{document}
\newcommand{\mywidth}{12cm}
\newcommand{\myheight}{5cm}

\pgfplotstableread[col sep=comma]{
seats, 2003, 2008
ordinary, 42.26, 52.16
premium, 275, 325
}\ticketprices

\begin{tikzpicture}[font=\sffamily\sansmath]

\begin{axis}[ 
      ybar=10pt,
      bar width=20pt,
      ymin=0,
      tick style={draw=none},
      width=\mywidth, height=\myheight, 
      title={Tickets at Fenway Park}, 
      hide y axis,
      axis x line*=bottom,
      xtick=data,
      xticklabel style={align=center},
      xticklabels={
        2003 2008\\
        ordinary seats,
        2003 2008\\
        premium seats
      },
      nodes near coords,
    ]
    \addplot [fill=gray] table[x expr=\coordindex, y=2003]  {\ticketprices};
    \addplot [fill=black] table[x expr=\coordindex, y=2008] {\ticketprices};
\end{axis} 
\end{tikzpicture}
\end{document}

Answer 1

You can decide what to print in the nodes near coords labels using the optional argument. By default, it's defined as nodes near coords=\pgfmathprintnumber{\pgfplotspointmeta}, so it's a pretty formatting of the value of \pgfplotspointmeta, which, by default, holds the current y value.

In your case, you could set

nodes near coords={\$\pgfmathprintnumber{\pgfplotspointmeta}}

to put a dollar sign in front of each value.

To make the plot width match the number of data series, the easiest thing to do is to define the x unit vector in terms of the bar width: If your bar width is 20pt, and the gap between the bars is ybar=15pt, you could set x={2*15pt+2*20pt+10pt} (two data series, two gaps, plus a little extra to separate the groups. To make sure the bars aren't cut off at the edges, you can set enlarge x limits={abs=20pt+15pt}, (space for one bar, plus another gap).

The solution scales as more plots are added:

\documentclass{standalone}
\usepackage{tikz,pgfplots}
\usepackage{pgfplotstable}

\usetikzlibrary{calc,decorations.pathmorphing}

%deal with warning message in log
\pgfplotsset{compat=1.8}

\usepackage{helvet}
\usepackage[eulergreek]{sansmath}

\begin{document}
\newcommand{\mywidth}{12cm}
\newcommand{\myheight}{5cm}

\pgfplotstableread[col sep=comma]{
seats, 2003, 2008
ordinary, 42.26, 52.16
premium, 275, 325
extreme, 800, 850
}\ticketprices

\begin{tikzpicture}[font=\sffamily\sansmath]

\begin{axis}[ 
      ybar=15pt,
      bar width=20pt,
      x={2*15pt+2*20pt+10pt},
      enlarge x limits={abs=20pt+15pt},
      ymin=0,
      tick style={draw=none},
      width=\mywidth, height=\myheight, 
      title={Tickets at Fenway Park}, 
      hide y axis,
      axis x line*=bottom,
      xtick=data,
      xticklabel style={align=center},
      xticklabels={
        2003 2008\\
        ordinary seats,
        2003 2008\\
        premium seats,
        2003 2008\\
        extreme deluxe
      },
      nodes near coords={\$\pgfmathprintnumber{\pgfplotspointmeta}},
    ]
    \addplot [fill=gray] table[x expr=\coordindex, y=2003]  {\ticketprices};
    \addplot [fill=black] table[x expr=\coordindex, y=2008] {\ticketprices};
\end{axis} 
\end{tikzpicture}
\end{document}