[datatable-help] Extract Single Column as Vector

[Alexandre Sieira]

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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.r-forge.r-project.org/pipermail/datatable-help/attachments/20130517/ff2b8745/attachment.html>