Yes but in base not in data.table : arr[as.matrix(dt)]
See FAQ 2.14 for how and why that inspired data.table. Matthew > Hi, I have an array like this: > arr<- array(c(1,2,2,1),c(2,2)) > > and a data.table like this: > dt<- data.table(a = c(1,1,2,2), b = c(1,2,1,2)) > > I'd like to add a column 'c' to dt that uses columns 'a' and 'b' as > indices to arr, like this: > dt$c<- apply(dt,1,function(x) arr[x['a'],x['b']]) > > That works fine, of course, but it is pretty slow and I need to do > this several times in each analysis I run. Is there a faster > data.table way to do this? > > sorry if this is such a basic question! > > Matthew > _______________________________________________ > 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
