[datatable-help] .I does not respect by

[Arunkumar Srinivasan]

Okay. Added a "Doc" tracker #5520.

Arun

From: Gabor Grothendieck ggrothendieck at gmail.com
Reply: Gabor Grothendieck ggrothendieck at gmail.com
Date: April 1, 2014 at 2:02:30 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  

Perhaps it could read .I = 1:nrow(x). Note that .I does not equal  
1:.N if there are groups.  


On Tue, Apr 1, 2014 at 7:57 AM, Arunkumar Srinivasan  
<aragorn168b at gmail.com> wrote:  
> 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  



--  
Statistics & Software Consulting  
GKX Group, GKX Associates Inc.  
tel: 1-877-GKX-GROUP  
email: ggrothendieck at gmail.com  
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