[datatable-help] Feature Idea

[Matthew Dowle]

(I think) it already does that. It's just that it sets a key on the
result by default (which does the re-ordering of the grouped results at
the end). If that's true, then could provide a way to not call setkey at
the end. There is also the 'bysameorder' argument which might already be
doing something similar.

Matthew 

On Fri, 2011-07-08 at 14:29 -0400, Steve Lianoglou wrote:
> Hi,
> 
> I find myself often wanting to use a data.table for its quick
> aggregate&summary mojo, but I want to keep the ordering of my data as
> I have it, and not as it would be if I set the appropriate keys for my
> aggregation/summary.
> 
> How would you folks feel if I add a `by` (or dt.by) method for a data.table, eg:
> 
> result <- by(some.data.table, would.be.keys, {
>  ## stuff
> }, ...)
> 
> Which does the aggregate/summary encoded within { ... }, but the
> result is returned in the same order as `some.data.table` was in when
> it was passed into the function -- if { ... } returned as many rows as
> were in the original data.table, then it's 1-for-1, but you are
> summarizing groups of rows, the summary would be in the same
> (appearance) order as it is in `some.data.table`.
> 
> The { ... } block would essentially be anything you can put in the `j`
> part of a data.table[i, j, ...].
> 
> The `...` dots after { ... } maybe extra params that can get passed
> into a "normal" data.table[i,j,...] call (haven't thought about that
> yet, tho).
> 
> If I can get some consensus on whether or not it's worthwhile to put
> such a function into the data.table package, I'll go ahead and add an
> initial implementation -- otherwise I can just keep it in my personal
> utility belt whenever I need to use it.
> 
> Thanks,
> -steve
>