multicore by(), like mclapply?

Hi Ivo,

My suggestion would be to only pass lapply (or mclapply) the indices.
That should be fast, subsetting with data table should also be fast,
and then you do whatever computations you will.  For example:

require(data.table)
DT <- data.table(x=rep(c("a","b","c"),each=3), y=c(1,3,6), v=1:9)
setkey(DT, x)

lapply(as.character(unique(DT[,x])), function(i) DT[i])

the DT[i] object is the subset of the data table you want.  You can
pass this to whatever function for computations you need.

Hope this helps,

Josh

dear r experts---Is there a multicore equivalent of by(), just like
mclapply() is the multicore equivalent of lapply()?

if not, is there a fast way to convert a data.table into a list based
on a column that lapply and mclapply can consume?

advice appreciated...as always.

regards,

/iaw
----
Ivo Welch (ivo.welch at gmail.com)

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Joshua Wiley
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Programmer Analyst II, ATS Statistical Consulting Group
University of California, Los Angeles
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