\begin{thebibliography}{2}
\providecommand{\natexlab}[1]{#1}
\providecommand{\url}[1]{\texttt{#1}}
\expandafter\ifx\csname urlstyle\endcsname\relax
  \providecommand{\doi}[1]{doi: #1}\else
  \providecommand{\doi}{doi: \begingroup \urlstyle{rm}\Url}\fi

\bibitem[Chambers(1998)]{R:Chambers:1998}
John~M. Chambers.
\newblock \emph{Programming with Data}.
\newblock Springer, New York, 1998.
\newblock ISBN 0-387-98503-4.

\bibitem[Koenker and Ng(2003)]{koen:ng:2003}
Roger Koenker and Pin Ng.
\newblock {SparseM}: A sparse matrix package for {R}.
\newblock \emph{J. of Statistical Software}, 8\penalty0 (6), 2003.

\end{thebibliography}