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
