[datatable-help] Extract Single Column as Vector

[Arunkumar Srinivasan]

Eduard, are we discussing the same thing again :)? Wasn't this somehow your question as well.. the discrepancy between:  

dt[, a] and dt[, "a", with=FALSE].  

There should be a drop=TRUE/FALSE option (as in the case of data.frame) that should be used when you use `with=FALSE`. Until then, the default option seems to be drop=FALSE, which results in a data.table.

Alexandre, as of now, it could be done as Eduard points out.  

Arun


On Friday, May 17, 2013 at 4:59 PM, Eduard Antonyan wrote:

> Use dt[[colname]], but this seems like a bug to me - I would've thought that dt[, a] and dt[, "a", with = F] should return the exact same thing.
>  
>  
> On Fri, May 17, 2013 at 9:42 AM, Alexandre Sieira <alexandre.sieira at gmail.com (mailto:alexandre.sieira at gmail.com)> wrote:
> >  
> > Sorry if this is a basic question.
> >  
> >  
> >  
> >  
> >  
> >  
> > I'm using R 3.0.0 and data.table 1.8.8. The documentation for 'j' states that "A single column or single expression returns that type, usually a vector."
> >  
> >  
> >  
> >  
> >  
> >  
> > I am able to obtain this behavior if I know the column name in advance:
> >  
> >  
> >  
> >  
> >  
> >  
> >  
> >  
> >  
> > > dt = data.table(a=c(1, 2, 3), b=c(4, 5, 6))
> >  
> >  
> > > dt
> >  
> >  
> >    a b
> >  
> >  
> > 1: 1 4
> >  
> >  
> > 2: 2 5
> >  
> >  
> > 3: 3 6
> >  
> >  
> > > str(dt[,a])
> >  
> >  
> >  num [1:3] 1 2 3
> >  
> >  
> >  
> >  
> >  
> >  
> > However, if I don't, no such luck:  
> >  
> > > colname="a"
> > > str(dt[,colname,with=F])
> > Classes ‘data.table’ and 'data.frame': 3 obs. of  1 variable:
> >  $ a: num  1 2 3
> >  - attr(*, ".internal.selfref")=<externalptr>  
> >  
> >  
> > If there a way to extract an entire column as a vector if I have the column name as a character scalar?  
> >  
> > Thank you!
> >  
> > --   
> > Alexandre Sieira
> > CISA, CISSP, ISO 27001 Lead Auditor
> >  
> > "The truth is rarely pure and never simple."
> > Oscar Wilde, The Importance of Being Earnest, 1895, Act I  
> > _______________________________________________
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>  
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