does this do what you want: > dt <-data.table(col1=c(1,2,3)) > dt col1 1: 1 2: 2 3: 3 > dt[2:nrow(dt), col3:=dt[1:(nrow(dt) - 1), list(col1)]>2] > dt col1 col3 1: 1 NA 2: 2 FALSE 3: 3 FALSE
Jim Holtman Data Munger Guru What is the problem that you are trying to solve? Tell me what you want to do, not how you want to do it. On Mon, Oct 19, 2015 at 9:59 AM, Nicolas Paris <[email protected]> wrote: > Hello, > > I wonder if there is a way in data.table (or more generaly in R) to work > on previous row without loops > E.G. something equivalent to : > > dt <-data.table(col1=c(1,2,3)) > for (i in 2:nrow(dt)) > { > dt[i,col3:=dt[i-1,list(col1)]>2] > } > > Thanks a lot ! > > _______________________________________________ > datatable-help mailing list > [email protected] > https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help >
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