Use of rnd in pgfplots

Question

The following code fails to compile due to the use of rnd:

\documentclass{article}
\usepackage{tikz,pgfplots}
\pgfplotsset{width=7cm,compat=1.3}
\begin{document}

\begin{tikzpicture}
\begin{axis}
\addplot {x};
    \draw [] (axis cs: 0,0)
      \foreach \i in {1,...,10} {
        -- ++ (axis direction cs: 0.2,rnd)
        };
   \end{axis}
\end{tikzpicture}
\end{document}

Why is this happening and how can it be rewritten to work as intended?

I believe that this has something to do with axis direction cs. Taking that out this compiles fine. Also, it is better to use article class and not minimal. See Why not use the minimal class. — Peter Grill, Feb 24 '13 at 19:16
@PeterGrill by removing axis direction cs it seems to compile, but I can't see any drawings however!!! — niels, Feb 24 '13 at 19:20

score 5 · Accepted Answer · answered Feb 24 '13 at 19:23

This is probably due to the coordinate parsing as rnd is not recognized as a math function but as a non-number instead. Bracing it or other syntax tricks might work but it's best to avoid them for such simple constructions.

Here is one option by removing the math parsing from the coordinate parsing. \pgfextra is used to pause the parsing and do some additional operations.

\documentclass{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.7}
\begin{document}
\begin{tikzpicture}
\begin{axis}
\addplot {x};
    \draw [] (axis cs: 0,0)
      \foreach \i in {1,...,10} {\pgfextra{\pgfmathparse{rnd}}
        -- ++ (axis direction cs: 0.2,\pgfmathresult)
        };
\end{axis}
\end{tikzpicture}
\end{document}

enter image description here

Use of rnd in pgfplots

1 Answers1