pgfplotstable: Why does `postproc cell content` not work properly when used within a style?

Question

I use pgfplotstable and want to post-format a specific column. Among other things I need to duplicate its content. My problem is that postproc cell content works fine as a direct parameter to pgfplotstabletypeset but not when I try to put it into a style so I can use it for multiple tables.

\documentclass[11pt]{article}
\usepackage{pgfplotstable}

\begin{document}
\begin{table}
\centering

\pgfplotstableread{
A   B   C
1   3.5 2.4
2   1.2 6.7
3   2.1 3.3
}\data

\pgfplotstableset{
 debug,
 mytable/.style={
  columns={A,B,C},
  columns/A/.style={string type,
                    postproc cell content/.style={
                     @cell content=\ensuremath{##1 \leftrightarrow ##1}
                    }
                   },
 }
}

\pgfplotstabletypeset[
    mytable,
%    columns/A/.style={string type,
%                      postproc cell content/.style={
%                       @cell content=\ensuremath{##1 \leftrightarrow ##1}
%                      }
%                     }
]{\data}

\caption{Some important table}
\end{table}

\end{document}

When I enable the commented lines it looks like it should, without them the original numbers are missing.

Sorry, cannot post images...

Answer 1

This is a little hard to explain ( you can even call it a bug) but each time an argument passes through a style an expansion of # is lost. So you need four # chars.

\documentclass[11pt]{article}
\usepackage{pgfplotstable}

\begin{document}
\begin{table}
\centering

\pgfplotstableread{
A   B   C
1   3.5 2.4
2   1.2 6.7
3   2.1 3.3
}\data

\pgfplotstableset{
 debug,
 mytable/.style={
  columns={A,B,C},
  columns/A/.style={string type,
                    postproc cell content/.style={
                     @cell content=\ensuremath{####1 \leftrightarrow ####1}
                    }
                   },
 }
}

\pgfplotstabletypeset[
    mytable,
%    columns/A/.style={string type,
%                      postproc cell content/.style={
%                       @cell content=\ensuremath{##1 \leftrightarrow ##1}
%                      }
%                     }
]{\data}

\caption{Some important table}
\end{table}

\end{document}