[R] 1.8.1 and subsetting dataframes

[Prof Brian Ripley]

The changes you point to were between 1.7.1 and 1.8.0, not between 1.8.0 
and 1.8.1.

1.7.1 was quite capable of producing invalid data frames from erroneous 
usages.

I think we really do need to see a reproducible example.

On Tue, 25 Nov 2003, Patrick Connolly wrote:

> I've encountered something that didn't arise using earlier versions of
> R (Linux).
> 
> A dataframe is created and new columns added to it by doing
> calculations using apply with various functions on some of the
> original columns.  It's somewhat too involved to give a toy example
> that's reproducible.  However, the resulting phenemonon can be
> characterised by the following:
> 
> Browse[1]> dim(mod.df)
> [1] 409   5
> Browse[1]> object.size(mod.df)
> [1] 31520
> Browse[1]> is.array(mod.df)
> [1] FALSE
> Browse[1]> mod.df[1:5,]
> Error in as.data.frame.default(x[[i]], optional = TRUE) : 
> 	can't coerce array into a data.frame
> 
> The whole dataframe would display correctly, so I figured it couldn't
> have much wrong with it.  So I tried this:
> 
> 
> Browse[1]>     write.table(mod.df, "mod.tmp", quote = F, sep = "\t", row.names = F)
> Browse[1]>     mod.df <- read.table("mod.tmp", T, sep = "\t")
> Browse[1]> is.array(mod.df)
> [1] FALSE
> Browse[1]> object.size(mod.df)
> [1] 16164
> Browse[1]> mod.df[1:5,]
>         Site System Cultivar  Type CFU
> 1 Canterbury    ifp braeburn fruit 388
> 2 Canterbury    ifp braeburn fruit 920
> 3 Canterbury    ifp braeburn fruit 868
> 4 Canterbury    ifp braeburn fruit 328
> 5 Canterbury    ifp braeburn fruit 656
> 
> 
> The size of the object using R-1.8.0 (which had no subsetting
> problems) was
> 
> Browse[1]> object.size(mod.df)
> [1] 21160
> 
> 
> I suspect it could have something to do with some of the changes
> mentioned in this part of the NEWS file:
> 
>     o	Subscripting for data.frames has been rationalized:
> 
> But I'm not smart enough to see what in those dozen or so would have a
> bearing on this case.  I don't think the drop argument comes into what
> I've done.
> 
> If that's not sufficient to give anyone a hint what could be
> happening, I'll have another attempt to get a toy version.
> 
> 
> Thanks.
> 
> PS: Is there a more elegant way using a text connection instead or
> creating a temporary file in my work around?

Yes!  Use an anonymous file connection opened for rw.


-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595