Thanks! - Elliot
From: [email protected] [mailto:[email protected]] On Behalf Of Frank Erickson Sent: Wednesday, August 16, 2017 6:24 PM To: Bernstein, Elliot J Cc: [email protected] Subject: Re: [datatable-help] Data Table Subset Question One idiom for testing group-level conditions is: data[, if (mean(x) < 10) .SD, by=g] This might be slower in the special case of taking a mean. See ?GForce. There's a request for an idiom like SQL HAVING over here: https://github.com/Rdatatable/data.table/issues/788 --Frank On Wed, Aug 16, 2017 at 4:44 PM, Bernstein, Elliot J <[email protected]<mailto:[email protected]>> wrote: Is there a way to subset a data table by the result of a grouped aggregation without adding an interim column to the table? For example, if I want to select all rows for which the group mean value of x is less than 10, I can do the following: data <- data.table(x = 1:20, g = rep(c("a", "b"), each = 10)) data[, mean.x := mean(x), by = .(g)] data[mean.x < 10,] But I’m not really interested in “mean.x”. Can I do the same thing without adding it to the table? Thanks. - Elliot _______________________________________________ datatable-help mailing list [email protected]<mailto:[email protected]> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
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