Forgot to reply to the list...
On Tue, Dec 7, 2010 at 2:07 PM, Matthew Dowle <[email protected]> wrote:
>
> Does anyone have time to see if this post uses data.table correctly :
>
> http://stackoverflow.com/questions/4322219/whats-the-fastest-way-to-merge-join-data-frames-in-r
Not enough time to do it justice. On my system, I get the following:
> system.time(aggregate <- aggregate(d[c("x", "y")], d[c("g1", "g2")], mean))
user system elapsed
6.72 0.08 6.65
> system.time(dt1 <- dt[, list(x=mean(x), y=mean(y)), by = "g1,g2"])
user system elapsed
3.95 0.02 3.87
> system.time(dt2 <- dt[, list(x=.Internal(mean(x)), y=.Internal(mean(y))), by
> = "g1,g2"])
user system elapsed
0.12 0.01 0.19
This is a "many groups" case.
- Tom
_______________________________________________
datatable-help mailing list
[email protected]
https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
