[datatable-help] .I does not respect by

[Arunkumar Srinivasan]

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 ggrothendieck at gmail.com
Reply: Gabor Grothendieck ggrothendieck at gmail.com
Date: April 1, 2014 at 1:45:39 PM
To: Arunkumar Srinivasan aragorn168b at gmail.com
Cc: datatable-help at lists.r-forge.r-project.org datatable-help at lists.r-forge.r-project.org
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  
<aragorn168b at gmail.com> 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 ggrothendieck at gmail.com  
> Reply: Gabor Grothendieck ggrothendieck at gmail.com  
> Date: April 1, 2014 at 1:09:23 PM  
> To: datatable-help at lists.r-forge.r-project.org  
> datatable-help at lists.r-forge.r-project.org  
> 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  
> datatable-help at lists.r-forge.r-project.org  
> 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  
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.r-forge.r-project.org/pipermail/datatable-help/attachments/20140401/e3d2d65d/attachment.html>