# Tikz : column header in groupplot legend with a loop

I'm trying to plot some data using loops, but i've some issues when I try to extract the column header and have it as a sub legend. Does anyone have any idea to fix it up ?

\documentclass{minimal}

\usepackage{tikz}
\usepackage{pgfplots}
\usepgfplotslibrary{groupplots}
\usepackage{pgfplotstable}
\definecolor{skyblue1}{rgb}{0.447,0.624,0.812}

time    y   c   q   r   pi  r_F efp z_E z_F
1   0.105597    0.000553    0.007493    0.002008    0.001352    41.251213   0.015177    0.015177    41.251213
2   0.003563    0.003143    -0.001881   0.000742    -0.000582   0.541130    -0.011564   -0.001644   0.545364
3   0.003204    0.004251    -0.000223   0.000048    -0.000367   -0.016199   0.000767    0.001246    -0.016337
4   0.003582    0.004518    0.000531    -0.000285   -0.000218   -0.115549   0.000642    0.000411    -0.115694
5   0.003762    0.004358    0.000743    -0.000414   -0.000126   -0.158629   0.000492    -0.000035   -0.158753
}\modelresponses
\pgfplotstablegetcolsof{\modelresponses}

\begin{document}
\begin{tikzpicture}

\begin{groupplot}[group style={group size=3 by 2,vertical sep= 1.5cm},width=0.45\textwidth,ybar]
\pgfplotsinvokeforeach{1,2,3,4,5,6,7,8,9}{%
\pgfplotstablegetcolumnnamebyindex{#1}\of{\modelresponses}\to{\mycolname};
\nextgroupplot[title=\mycolname,grid=major];
\addplot[very thick,smooth,skyblue1] table [ x index=0,  y index=#1] {\modelresponses};
}
\end{groupplot}
\end{tikzpicture}
\end{document}

-
Just to make your example compilable, replace the group title key with title=$\mycolname$. –  percusse Jun 7 '12 at 14:17
@percusse: I believe that's the answer to the question =) –  Jake Jun 7 '12 at 14:23
@percusse found the solution. It's now working, thanks a lot. –  gVermandel Jun 7 '12 at 14:44

\nextgroupplot[title=$\mycolname$,grid=major];

However, just for the sake of curiosity it would be nice if someone can find a way to pass the title names including math characters like \pi,\psi without expanding (as I suspect it is the problem).
Christian Feuersänger showed a way how to do this in How can LaTeX code in a data file be read by pgfplotstable?: You define a macro \let\ESCAPE=\string at the start of the file, change the column name in the datafile to {\ESCAPE\pi}, and use title=\let\ESCAPE\relax$\mycolname$. –  Jake Jun 7 '12 at 15:39