Strange interaction between `addlegendentry` and `y filter` in pgfplot

Question

From this answer How to scale existing coordinates data in pgfplots? I am using y filter to process data, all fine until I decide to put a legend entry in the plot. I cannot seem to simultaneously use the yfilter and the addlegendenty lines in the following code.

I get this error

! Illegal parameter number in definition of \pgfplots@curplotlist.

from this code (later try commenting the two lines):

\documentclass{article}
\usepackage{pgfplots}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\begin{axis}
\addplot[
    y filter/.code={\pgfmathparse{#1*10.}\pgfmathresult}% try comment
] coordinates {
 ( 1., 1. )
 ( 2., 2. )
 ( 3., 3. )
};
\addlegendentry{Legend Entry};% try comment
\end{axis}
\end{tikzpicture}
\end{document}

What is wrong, is this a bug?

info: pdfTeX 3.1415926-2.5-1.40.14 LuaTeX, Version beta-0.76.0-2013061217 (TeX Live 2013)

Answer 1

It turns out that this is due to a somewhat quirky behaviour of x filter that's described in the manual:

Note that you can provide different x filter/y filter arguments to each \addplot command. It seems there are only problems with the #1 argument, and I haven’t yet found out why. Please use \pgfmathresult in place of #1 if you provide \addplot[x filter/.code={...}].

So if you change your code to use

y filter/.code={\pgfmathparse{\pgfmathresult*10.}\pgfmathresult}

instead of

y filter/.code={\pgfmathparse{#1*10.}\pgfmathresult}

everything works as expected:

\documentclass{article}
\usepackage{pgfplots}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\begin{axis}
\addlegendentry{Legend Entry};
\addplot[
    y filter/.code={\pgfmathparse{\pgfmathresult*10.}\pgfmathresult}
] coordinates {
 ( 1., 1. )
 ( 2., 2. )
 ( 3., 3. )
};
\end{axis}
\end{tikzpicture}
\end{document}