where ... is eval(myid) iigc > Or: > DT[,lapply(.SD,sum),by=...,.SDcols=myvars] > >> with = FALSE will let you use literal column names >> >> >> On Wed, Apr 24, 2013 at 3:29 PM, Sam Steingold <[email protected]> wrote: >> >>> What do I do if I want to operate on several columns? >>> E.g., >>> --8<---------------cut here---------------start------------->8--- >>> length(names(dt)) = 25 >>> myvars = c("col1","col4","col7") >>> myid = "user" >>> setkeyv(dt,myid) >>> --8<---------------cut here---------------end--------------->8--- >>> and I want to summarize columns in myvars by myid. >>> the point is that nowhere in the code the literal "col4" or "user" may >>> appear. >>> >>> Thanks. >>> >>> -- >>> Sam Steingold (http://sds.podval.org/) on Ubuntu 12.10 (quantal) X >>> 11.0.11300000 >>> http://www.childpsy.net/ http://ffii.org http://palestinefacts.org >>> http://openvotingconsortium.org http://camera.org http://jihadwatch.org >>> The difference between genius and stupidity is that genius has its >>> limits. >>> _______________________________________________ >>> datatable-help mailing list >>> [email protected] >>> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help >>> >> _______________________________________________ >> datatable-help mailing list >> [email protected] >> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help > > > _______________________________________________ > datatable-help mailing list > [email protected] > https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help >
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