[datatable-help] behavior of unique on data.tables with strings

[Matthew Dowle]

Ok thanks. Please file a bug report (mentioning it might be a 64bit
and/or mac only problem), so it's not forgotten. Trying to fix the Chris
crash so will have to come back to it ...

On Mon, 2012-01-02 at 20:13 -0800, Steven C. Bagley wrote:
> It still happens. (I deleted R and all packages, then reinstalled just to check.) 
> 
> test.data.table() completes without errors. 
> 
> Here's the session info.
> 
> > sessionInfo()
> R version 2.14.0 (2011-10-31)
> Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit)
> 
> locale:
> [1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8
> 
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods   base     
> 
> other attached packages:
> [1] data.table_1.7.7
> 
> > .Machine$double.eps ^ 0.5
> [1] 1.490116e-08
> 
> --Steve
> 
> On Jan 2, 2012, at 3:27 PM, Matthew Dowle wrote:
> 
> > Thanks for the nice report. Oddly though, it seems to work ok for me
> > both in 1.7.7 and latest 1.7.8.
> > 
> > $ R --vanilla
> > R version 2.14.1 (2011-12-22)
> > Platform: i686-pc-linux-gnu (32-bit)
> >> require(data.table)
> > Loading required package: data.table
> > data.table 1.7.7  For help type: help("data.table")
> >> foo2=as.data.table(data.frame(a=c("1", "1"), b=c(2,2),
> > stringsAsFactors=FALSE)) 
> >> unique(foo2)
> >     a b
> > [1,] 1 2
> >> str(foo2)
> > Classes ‘data.table’ and 'data.frame':	2 obs. of  2 variables:
> > $ a: chr  "1" "1"
> > $ b: num  2 2
> >> .Machine$double.eps ^ 0.5
> > [1] 1.490116e-08
> > 
> > Could you rerun and confirm please. If you are 64bit, please include
> > sessionInfo(). I've included tolerance as a long shot - the numeric 2's
> > are considered equal by data.table's unique() using tolerance. Perhaps
> > that part is not working for you. Does test.data.table() work? It should
> > test unique and tolerance fairly thoroughly. Otherwise I can't think why
> > the character column isn't liked by unique, should be ok.
> > 
> > A fast unique for character columns is a good feature request, please
> > could you add to the tracker. That is now possible to implement as we
> > now have fast character methods.
> > 
> > Matthew
> > 
> > On Mon, 2011-12-26 at 19:33 -0800, Steven C. Bagley wrote:
> >> In data.table 1.7.7: 
> >> 
> >> The function unique works for datatables (without keys) that have factors, but not if they have strings. In the latter case, setting the key will convert the strings to factors. I can't figure out from the documentation if this is the intended behavior or not. (The documentation does say that keys can't be characters/strings). It would be nice if unique would work without having to convert strings to factors because of the conversion cost in very large datatables, but maybe this isn't possible.
> >> 
> >> --Steve
> >> 
> >>> library(data.table)
> >>> foo1=as.data.table(data.frame(a=c("1", "1"), b=c(2,2)))
> >>> foo1
> >>     a b
> >> [1,] 1 2
> >> [2,] 1 2
> >>> str(foo1)
> >> Classes ‘data.table’ and 'data.frame':	2 obs. of  2 variables:
> >> $ a: Factor w/ 1 level "1": 1 1
> >> $ b: num  2 2
> >>> unique(foo1)
> >>     a b
> >> [1,] 1 2
> >>> foo2=as.data.table(data.frame(a=c("1", "1"), b=c(2,2), stringsAsFactors=FALSE))
> >>> foo2
> >>     a b
> >> [1,] 1 2
> >> [2,] 1 2
> >>> str(foo2)
> >> Classes ‘data.table’ and 'data.frame':	2 obs. of  2 variables:
> >> $ a: chr  "1" "1"
> >> $ b: num  2 2
> >>> unique(foo2)
> >>     a b
> >> [1,] 1 2
> >> [2,] 1 2
> >>> setkey(foo2, a)
> >>> str(foo2)
> >> Classes ‘data.table’ and 'data.frame':	2 obs. of  2 variables:
> >> $ a: Factor w/ 1 level "1": 1 1
> >> $ b: num  2 2
> >> - attr(*, "sorted")= chr "a"
> >>> unique(foo2)
> >>     a b
> >> [1,] 1 2
> >> _______________________________________________
> >> 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
> > 
> > 
>