[datatable-help] Fwd: Sum on colunms by a reference column

[Steve Lianoglou]

Hi,

On Thu, Jul 21, 2011 at 3:27 AM, Emmanuel Blondel
<emmanuel.blondel1 at gmail.com> wrote:
> Dear all,
>
> I have a datatable (mydt) with a reference column (code) for which I set a
> key, and a set of numeric columns (A ,B, C, D, E).
> I obtain this from a serie of script codes, but the issue is that I have
> duplicated rows (code), So i want to do is according to codestation, for
> each of the columns..
>
> I could do the following code for one single column:
> result<-mydt[,sum(A),by=code]
>
> but I would like to know if it is possible to do it for each of the columns,
> so I get a databable with the same columns with sum value, group by
> codestation. Do you have any suggestion?

Do you mean something like:

R> mydt[, list(A=sum(A), B=sum(B), C=sum(C), D=sum(D), E=sum(E)), by=code]

or equivalently, but maybe slower (there is a recent thread on the
list about this):

R> mydt[, lapply(.SD, sum), by=code]

Is that what you are after?

-steve

-- 
Steve Lianoglou
Graduate Student: Computational Systems Biology
 | Memorial Sloan-Kettering Cancer Center
 | Weill Medical College of Cornell University
Contact Info: http://cbio.mskcc.org/~lianos/contact