[R] multicore by(), like mclapply?

[Thomas Lumley]

On Tue, Oct 11, 2011 at 7:54 AM, ivo welch <ivo.welch at gmail.com> wrote:
> hi josh---thx.  I had a different version of this, and discarded it
> because I think it was very slow.  the reason is that on each
> application, your version has to scan my (very long) data vector.  (I
> have many thousand different cases, too.)  I presume that by() has one
> scan through the vector that makes all splits.

 by.data.frame() is basically a wrapper for tapply(), and the key line
in tapply() is
   ans <- lapply(split(X, group), FUN, ...)
which should be easy to adapt for mclapply.

-- 
Thomas Lumley
Professor of Biostatistics
University of Auckland