Hello,
I'm trying to group a data.table that has duplicate keys, aggregating
the values in another column by the value of the key.
There is a question and answer on the same topic on StackOverflow
(http://stackoverflow.com/a/17033371/3017012), but when I follow the
accepted answer I get different results:
> library(data.table)
data.table 1.9.2 For help type: help("data.table")
> dt = data.table(user_id = c(1,2,2,3), advertiser_id = c(1:4))
> dt[,list(list(advertiser_id)), by = user_id]
user_id V1
1: 1 4,3
2: 2 4,3
3: 3 4,3
Where I expect:
user_id V1
1: 1 1
2: 2 2,3
3: 3 4
I can get the expected results (as above) using:
> dt[,paste(advertiser_id, collapse = ","), by = user_id]
Have I missed something? I'm on R 3.1.1 in case the behaviour has
changed recently.
Many thanks,
Tom
_______________________________________________
datatable-help mailing list
[email protected]
https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
