[datatable-help] Extract Single Column as Vector

[Eduard Antonyan]

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> 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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