[datatable-help] rbindlist and factors

[Arunkumar Srinivasan]

This was already addressed here:  
http://stackoverflow.com/questions/15933846/rbindlist-two-data-tables-where-one-has-factor-and-other-has-character-type-for

And was known to be a bug filed here:
https://r-forge.r-project.org/tracker/index.php?func=detail&aid=2650&group_id=240&atid=975

Which has been fixed in the current development version 1.8.9. (
Fixed by commit 879 in v1.8.9



Hope this helps,
Arun


On Tuesday, May 21, 2013 at 8:06 PM, Alexandre Sieira wrote:

> I think I found an unexpected behavior with rbindlist when columns are factors:
>  
> > dt1 = data.table(a=as.factor(c("a", "a", "a")))
>  
> > dt1
>    a
> 1: a
> 2: a
> 3: a
> > str(dt1)
> Classes ‘data.table’ and 'data.frame': 3 obs. of  1 variable:
>  $ a: Factor w/ 1 level "a": 1 1 1
>  - attr(*, ".internal.selfref")=<externalptr>  
> > dt2 = data.table(a=as.factor(c("b", "b", "b")))
> > dt2
>    a
> 1: b
> 2: b
> 3: b
> > str(dt2)
> Classes ‘data.table’ and 'data.frame': 3 obs. of  1 variable:
>  $ a: Factor w/ 1 level "b": 1 1 1
>  - attr(*, ".internal.selfref")=<externalptr>  
>  
> If I rbind them, I get the expected value - a table with 6 rows, 3 of which have value "a" and 3 with value "b":
>  
> > rbind(dt1, dt2)
>    a
> 1: a
> 2: a
> 3: a
> 4: b
> 5: b
> 6: b
>  
>  
> So if I do rbindlist(list(dt1, dt2)), I would expect to get the exact same result, only faster. Unfortunately, that is not the case:
>  
> > rbindlist(list(dt1, dt2))
>    a
> 1: a
> 2: a
> 3: a
> 4: a
> 5: a
> 6: a
>  
> > str(rbindlist(list(dt1, dt2)))
> Classes ‘data.table’ and 'data.frame': 6 obs. of  1 variable:
>  $ a: Factor w/ 1 level "a": 1 1 1 1 1 1
>  - attr(*, ".internal.selfref")=<externalptr>  
>  
>  
> This was executed with R 3.0.1 and data.table 1.8.8 on a Mac OS X 10.8.3.
>  
> Is this expected behavior? Am I missing something?
>  
>  
>  
> --  
> Alexandre Sieira
> CISA, CISSP, ISO 27001 Lead Auditor
>  
> "The truth is rarely pure and never simple."
> Oscar Wilde, The Importance of Being Earnest, 1895, Act I
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