Unknown operator | when using data visualization and tikz

Question

Problem:

I am trying to get the function y = |x| to work with data visualization library in TikZ but without success. It seems the issue is with the operator |.

Minimal Working Example (MWE):

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{datavisualization}
\usetikzlibrary{datavisualization.formats.functions}
\begin{document}

\begin{tikzpicture}
    \datavisualization [school book axes,
                        visualize as smooth line,
                        y axis={label},
                        x axis={label}]

    data [format=function] {
          var x : interval [-5:5];
          func y = |x|;
    };
\end{tikzpicture}

\end{document}

Desired output:

To get the function to work with the operator |.

Answer 1

The vertical bars are just notation, i.e. a common way to typeset the absolute value. According to section 94.3 Syntax for Mathematical Expressions: Functions of the pgf manual (version 3.1.3) the function is abs (and you forgot a \value).

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{datavisualization}
\usetikzlibrary{datavisualization.formats.functions}
\begin{document}

\begin{tikzpicture}
    \datavisualization [school book axes,
                        visualize as smooth line,
                        y axis={label},
                        x axis={label}]

    data [format=function] {
          var x : interval [-5:5];
          func y = abs(\value x);
    };
\end{tikzpicture}

\end{document}

ADDENDUM: Can one declare new math operators? Yes. Can one define an operator |? Yes. Does it work as you want it and is it safe? Maybe not.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{datavisualization}
\usetikzlibrary{datavisualization.formats.functions}
\pgfmathdeclareoperator{|} {abs}   {1}{infix} {600}
\begin{document}
\begin{tikzpicture}
    \datavisualization [school book axes,
                        visualize as smooth line,
                        y axis={label},
                        x axis={label}]

    data [format=function] {
          var x : interval [-5:5];
          func y = | \value x ;
    };
\end{tikzpicture}

\end{document}