\documentclass[tikz,a4paper]{standalone}

\usepackage{tikz}

\begin{document}

\usetikzlibrary{datavisualization}

\begin{tikzpicture}
  \datavisualization[visualize as smooth line]
  data {
    x, y
    2, 1,
    3, 2,
    4, 1.5
  };
\end{tikzpicture}

\end{document}