The key part is "row locations in x". If it were to reset for each group, then that part wouldn't have been necessary. Perhaps it'd be clearer if it were something like this: ".I is an integer vector which, for each group, holds the corresponding row numbers in/from/of x"? Not sure which preposition is most appropriate here.
Arun From: Gabor Grothendieck [email protected] Reply: Gabor Grothendieck [email protected] Date: April 1, 2014 at 1:45:39 PM To: Arunkumar Srinivasan [email protected] Cc: [email protected] [email protected] Subject: Re: [datatable-help] .I does not respect by From the documentation I would have expected that the row locations start over at 1 for each group so that .I = 1:.N. but these are not equivalent. On Tue, Apr 1, 2014 at 7:20 AM, Arunkumar Srinivasan <[email protected]> wrote: > Gabor, > > It's the same as in 1.8.10 and 1.9.2. What is contradicting in ?data.table? > It says under .I: ".I is an integer vector length .N holding the row > locations in x for this group." > > The row locations in x for b=1,2,1,2 are 1,2,3,4 which then becomes 1,3 and > 2,4 for this group => b=1 and b=2 respectively. > > > Arun > > From: Gabor Grothendieck [email protected] > Reply: Gabor Grothendieck [email protected] > Date: April 1, 2014 at 1:09:23 PM > To: [email protected] > [email protected] > Subject: [datatable-help] .I does not respect by > > In the following .I seems not to be within group. > >> dt <- data.table(a = 1:4, b = 1:2) >> dt[, .I, by = b] > b .I > 1: 1 1 > 2: 1 3 > 3: 2 2 > 4: 2 4 >> packageVersion("data.table") > [1] '1.9.3' > > This seems contrary to ?data.table. > > > -- > 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 -- Statistics & Software Consulting GKX Group, GKX Associates Inc. tel: 1-877-GKX-GROUP email: ggrothendieck at gmail.com
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