Group style key does not work in pgfplotsset

Question

When I want to set a style using groupplot, I will do something like this:

\begin{groupplot}[
  group style={
    group size=1 by 2,
    vertical sep=1cm,
  },
]

However, I've found that if I try to save that as a style using pgfplotsset, like so:

\pgfplotsset{
  mygroup/.style={
    group style={
      group size=1 by 2,
      vertical sep=1cm,
    },
  },
}

applying the style seems to ignore the contents of the group style key. The value of other keys are observed and correctly applied, but not that of group style. If I want to make changes to the keys in the group path, I have to specify them entirely:

\pgfplotsset{
  mygroup/.style={
    group/group size=1 by 2,
    group/vertical sep=1cm,
  },
}

But this seems to me to be an odd, non-standard behaviour, since you wouldn't use this way of writing when specifying options to \begin{groupplot}.

Is this the expected behaviour? What is the recommended way to define group styles in pgfplotsset? Here's a MWE, where you can uncomment the different options:

\documentclass{article}
\usepackage{pgfplots}
\usetikzlibrary[pgfplots.groupplots,calc]

\pgfplotsset{
  compat=1.12,
  mygroup/.style={
    group style={
      group size=1 by 2,
      vertical sep=1cm,
    },
    every axis plot/.append style={
      smooth,
    }
  },
  mygroupb/.style={
    group/group size=1 by 2,
    group/vertical sep=1cm,
    every axis plot/.append style={
      smooth,
    }
  },
}

\begin{document}

\begin{figure}
  \centering
  \begin{tikzpicture}
    \begin{groupplot}[
        % This style works without "group style"
        % mygroupb,
        % This style doesn't apply "group style"
        % mygroup,
        % But adding it manually here works
        % group style={
        %   group size=1 by 2,
        %   vertical sep=1cm,
        % },
      ]  
      \nextgroupplot
        \addplot+[samples=5,domain=-3:3] {exp(-x^2+1)};
        \addplot+[samples=5,domain=-3:3] {exp(-x^2)};
        \addplot+[samples=5,domain=-3:3] {exp(-x^2-1)};

      \nextgroupplot
        \addplot+[samples=5,domain=-3:3] {exp(-x^2+1)};
        \addplot+[samples=5,domain=-3:3] {exp(-x^2)};
        \addplot+[samples=5,domain=-3:3] {exp(-x^2-1)};
    \end{groupplot}
  \end{tikzpicture}
\end{figure}

\end{document}

Answer 1

The problem is actually simpler than I used to think.

In the definition of \begin{groupplot}[#1] we see the following

\pgfkeysinstallkeyfilter{/pgf/key filters/equals}{/pgfplots/group style}%
\pgfkeysinstallkeyfilter{/pgf/key filters/is descendant of}{/pgfplots/group}%
\pgfqkeysfiltered{/pgfplots}{#1}%

Intuitively it tells that

• if you say [group style=something] then it is processed;
• if you say [group/something=else] then it is processed;
• otherwise the key is ignored.

And through some experiments what it really says is that

• if you say [group style=something] then it is processed;
  • if you say [mygroup], which is defined to be the same as above, then it is ignored.
• if you say [group/something=else] then it is processed;
  • if you say [mygroup], which is defined to be the same as above, then it is processed.
• otherwise the key is ignored.

I am afraid there is no easy way to fix this. Filtering is one of the core features of pgfkeys. Maybe there exists a trick playing around with .cd and .retry and so on. I cannot tell.

After all, pgfkeys does a lot of bizarre things. For example the manual claims that

There is exactly one key filter in effect, and it is installed by the .install key filter handler or by \pgfkeysinstallkeyfilter.

But here it just installs two filters.