[R] problem of data manipulation

[hadley wickham]

> Note that in the documentaton ?"[.data.table" where I say that 'by' is slow,
> I mean relative to how fast it could be.  Its seems, in this specific
> example anyway, and with the code posted so far, to be significantly faster
> than sqldf and plyr.

Of course the best of both worlds would be to use data table within
plyr to get both speed and a consistent syntax for other types of
split-apply-combine tasks.

Hadley


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