[datatable-help] .I does not respect by

[Gabor Grothendieck]

>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.
>
>
> --
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> email: ggrothendieck at gmail.com
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