[datatable-help] rbindlist and factors

[Alexandre Sieira]

Thank you, I'll wait for the next release then. 

It's do.call("rbind", …) till then, I presume. :)

-- 
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
On 21 de maio de 2013 at 15:09:00, Arunkumar Srinivasan (aragorn168b at gmail.com) wrote:
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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