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Problem with lme4 use and installation

On Mon, Mar 3, 2008 at 9:57 AM, Charilaos Skiadas <cskiadas at gmail.com> wrote:
Exactly.

The warning actually comes from loading the Matrix package, a package
is required by the lme4 package.  Martin Maechler and I define an
extended xtabs function as an S4 generic in the Matrix package.  This
version allows an optional argument "sparse".  When sparse = TRUE the
new version produces a cross-tabulation in the form of a sparse
matrix.  As you might expect, this is particularly useful for sparse
cross-tabulations.

When sparse = FALSE, the default value, this version reverts to the
xtabs function from the stats package.  Thus the substitution should
be benign except that it will make xtabs run infinitesimally slower
because it requires an extra level of dispatch.  Unless you are making
thousands of calls to xtabs you shouldn't notice this.