\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}