Problem with pgf-pie and \newcommand use

Question

I am currently using pgf-pie package and I face a problem when I write the pgf-pie content using \newcommand instruction. The following MWE

\documentclass{standalone}
\usepackage{pgf-pie}
\usetikzlibrary{shadows}
\begin{document}

\newcommand{\testpie}{10/ A , 20/ B , 30/ C , 40/ D}

\begin{tikzpicture}

\begin{pie}[
  text = inside,
  scale font,
  style = drop shadow
]
{
  \testpie
}
\end{pie}
\end{tikzpicture}

\end{document}

generates the following error

! Package PGF Math Error: Unknown function `A' (in '10/ A , 20/ B , 30/ C , 40/D').

The final goal is to automatically generate the "fraction" sequence by reading a pgfplotstable.

Edit:

Going back to initial code I have something like that

\documentclass{standalone}

\usepackage{pgfplotstable}
\usepackage{pgf-pie}
\usepackage{xstring}

\pgfplotstableread[col sep=comma]{
  Year,TB,B,AB,P,NA
  2008/2009,15,38,15,0,31
  2009/2010,13,25,38,0,25
  2010/2011,17,50,8,17,8
}{\mention}

%% Feel free to improve the next lines
\newcommand{\pieplot}[1]{%
  \pgfplotstableforeachcolumnelement{Year}\of{#1}\as\cell{%
    \IfStrEq{\cell}{2008/2009}{%
      \pgfplotsforeachungrouped \x in {TB,B,AB,P,NA}{%
        \pgfplotstablegetelem{\pgfplotstablerow}{\x}\of{#1}
        \pgfmathtruncatemacro\val{\pgfplotsretval}
        \ifnum\val=0
        \else
        \val / \x
        \IfStrEq{\x}{NA}{}{,}
        \fi
      }
    }
  }
}

\begin{document}
  \pieplot{\mention}
\end{document}

which generates the right "fraction" sequence but fails when I use \pie command even with \mypie command.

Answer 1

Based on the rudimentary documentation and related to the code of pgf-pie the mandatory argument will be passed directly to a foreach construction. So you have to fully expand the argument first. Here a suggestion by providing a new command \mypie:

\newcommand\mypie[2][]{%
 \begingroup
  \edef\x{\endgroup\noexpand\pie[#1]{#2}}
 \x}

Here the complete code:

\documentclass{standalone}
\usepackage{pgf-pie}

\begin{document}

\newcommand{\testpie}{10/ A , 20/ B , 30/ C , 40/ D}

\newcommand\mypie[2][]{%
 \begingroup
  \edef\x{\endgroup\noexpand\pie[#1]{#2}}
 \x}


\begin{tikzpicture}
\mypie{\testpie}
\end{tikzpicture}

\end{document}