[datatable-help] BUG: droplevels mangles subsetted data.table

[Steve Lianoglou]

Hi,

I see what the problem is -- we need to provide a
droplevels.data.table S3 method, because the way the
droplevels.data.frame method works isn't compatible with data.table
indexing.

Will fix:

https://r-forge.r-project.org/tracker/index.php?func=detail&aid=1841&group_id=240&atid=975

Thanks for raising the flag.

Cheers,
-steve

On Tue, Feb 21, 2012 at 12:38 PM, pchalasani <pchalasani at gmail.com> wrote:
>  Surprising that this wasn't noticed before, or perhaps I'm not following
> some recommended idiom to drop levels when using  data.table. The following
> code illustrates the bug clearly: The bug remains regardless of whether I
> use "subset" or simply use dt1 = dt[ name != 'a' ].
>
>
>
>    d <- data.table(name = c('a','b','c'), value = 1:3)
>    dt <- data.table(d)
>    setkey(dt,'name')
>    dt1 <- subset(dt,name != 'a')  # or dt1 <- dt[ name != 'a' ]
>    > dt1
>          name value
>     [1,]    b     2
>     [2,]    c     3
>
>    > droplevels(dt1)
>          name value
>     [1,]    b     1
>     [2,]    c     3
>
>
>
> --
> View this message in context: http://r.789695.n4.nabble.com/BUG-droplevels-mangles-subsetted-data-table-tp4407694p4407694.html
> Sent from the datatable-help mailing list archive at Nabble.com.
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-- 
Steve Lianoglou
Graduate Student: Computational Systems Biology
 | Memorial Sloan-Kettering Cancer Center
 | Weill Medical College of Cornell University
Contact Info: http://cbio.mskcc.org/~lianos/contact