[datatable-help] unique.data.frame should create a copy, right?

[Arunkumar Srinivasan]

Steve, 

Yes, exactly. If you dint have to subset the data.table as in your example, the equivalent operation would be to set the key of DT1 to NULL and then doing `unique` and storing it in DT2 and then setting the key back to "A" on DT1.

And it'd be nice to be able to do: `unique(DT1, usekey=FALSE)` or something like that so that we don't have to NULL and set the key of DT1. 

Arun


On Wednesday, July 31, 2013 at 8:02 PM, Steve Lianoglou wrote:

> Hi all,
> 
> On Wed, Jul 31, 2013 at 9:09 AM, Arunkumar Srinivasan
> <aragorn168b at gmail.com (mailto:aragorn168b at gmail.com)> wrote:
> > Ricardo,
> > 
> > You read my mind.. :) I was thinking of the same as well.. Whether the
> > community agrees or not would be interesting as well. It could save trouble
> > with "alloc.col" manually.
> > 
> 
> 
> It's easy enough to add -- just to be sure, the behavior required from
> the OP would be equivalent to calling unique on a data.table that has
> no key, right? For example, instead of this:
> 
> R> DT1 <- CJ(A=0:1,B=1:6,D0=0:1,D=0:1)[D>=D0]
> R> setkey(DT1,A)
> R> DT2 <- unique.data.frame(DT1[,-which(names(DT1)%in%'B'),with=FALSE])
> R> DT2[,gah:=1] # warning: I should have made a copy, apparently
> 
> You could just do:
> 
> R> DT1 <- CJ(A=0:1,B=1:6,D0=0:1,D=0:1)[D>=D0]
> R> DT2 <- unique(DT1[, -which(names(DT1)%in%'B'), with=FALSE])
> R> DT2[,gah:=1]
> 
> Right?
> 
> -steve
> 
> -- 
> Steve Lianoglou
> Computational Biologist
> Bioinformatics and Computational Biology
> Genentech
> 
> 


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