In this case? Then nothing'll be different. I'm not sure what you mean because the problem here is that this *doesn't* require *by-without-by* as the j-operations are not necessary to be performed *during* the join. So, we can just perform the join and then take the "abs" once at the end, rather than calling it about 1e5+ times (the number of groups).
So, if your question is: "apart from this question, how would an explicit by-without-by look like?", then I guess it'd be the same as the normal aggregation, but "by" would take a data.table as well. This has not yet been discussed or conceptualised. But this is how I imagine it to be: DT1[, list(...), by=DT2] Where, DT1's key columns have to be set as usual. On Thu, Feb 6, 2014 at 12:55 PM, Gabor Grothendieck <[email protected] > wrote: > On Wed, Feb 5, 2014 at 10:42 AM, Arunkumar Srinivasan > <[email protected]> wrote: > > Seems like the "by-without-by" is what's slowing things down: > > > > require(data.table) > > dtx <- data.table(x=which(X), key="x") > > dty <- data.table(y=which(Y), key="y") > > dtx[, x1 := x] > > dty[, y1 := y] > > system.time(ans <- dty[dtx, roll="nearest"][, abs(x1-y1)]) > > user system elapsed > > 1.321 0.076 1.396 > > system.time(ans2 <- flodel(x,y)) > > user system elapsed > > 0.936 0.044 0.977 > > > > identical(ans, ans2) # [1] TRUE > > What will the code look like after the explicit by-without-by feature is > added? > > -- > Statistics & Software Consulting > GKX Group, GKX Associates Inc. > tel: 1-877-GKX-GROUP > email: ggrothendieck at gmail.com >
_______________________________________________ datatable-help mailing list [email protected] https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
