Thanks Steve,
Though it is slower yes, it corresponds to what I was looking for. I
don't work with a very large amount of data, so the second option is
appropriate for me, at least at this stage.
Thanks a lot again,
Regards,
Emmanuel
Le 21/07/2011 15:15, Steve Lianoglou a écrit :
Hi,
On Thu, Jul 21, 2011 at 3:27 AM, Emmanuel Blondel
<[email protected]> 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
--
*Emmanuel Blondel*
GIS Consultant
Geographic Information Systems
in Agronomy - Environment -Fisheries
Email: [email protected] - [email protected]
Phone: +33 (0) 6 45 97 87 52
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