[datatable-help] No error on invalid assignment

[Stavros Macrakis]

Matthew,

Thanks for the reply.  It turns out that the problem I was reporting was in
data.table version 1.6.6, R version 2.13.1.    The issue is fixed in 1.7.1,
the current version. I should know better than to report problems without
version numbers (and without checking if there is a more recent version).
 Sorry for the noise.

            -s

On Fri, Oct 28, 2011 at 20:53, Matthew Dowle <mdowle at mdowle.plus.com> wrote:

> On Fri, 2011-10-28 at 18:46 -0400, Stavros Macrakis wrote:
> > > t1 <- data.table(a=1:3,b=1/(1:3))
> > > t1[1,2]<- 99
> >
> >
> > Shouldn't this give an error?
> Why? What else could it mean other than what it does :
> > t1
>     a         b
> [1,] 1 1.0000000
> [2,] 2 0.5000000
> [3,] 3 0.3333333
> > t1[1,2]<- 99
> > t1
>     a          b
> [1,] 1 99.0000000
> [2,] 2  0.5000000
> [3,] 3  0.3333333
>
>
> > With with=T (the default), this doesn't make sense, and the resulting
> > DT is not valid:
>
> The [<- method is different to the [ method of data.table.
>
> >
> >
> > > t1
> > Error in data.table(lapply(x, function(x) { :
> >   every input must have at least one value, unless all columns are
> > empty
>
> I can't reproduce this. I got a different (correct) error :
> > t1[1,2,with=FALSE]<- 99
> Error in `[<-.data.table`(`*tmp*`, 1, 2, with = FALSE, value = 99) :
>  unused argument(s) (with = FALSE)
>
>
> >
> >
> > In fact, I'm not sure how to modify an individual cell in a DT:
>
> It already did, above.  But, := is faster and shorter than <-.
>
> >
> >
> > > t1 <- data.table(a=1:3,b=1/(1:3))
> > > t1[1,2,with=F]<- 99
> > Error in `[<-.data.table`(`*tmp*`, 1, 2, with = F, value = 99) :
> >   unused argument(s) (with = F)
> >
> >
> > On the other hand, you can apparently modify an entire column:
> >
> >
> > t1 <- data.table(a=1:3,b=1/(1:3))
> > > t1$b <- 11:13
> > > t1
> >      a  b
> > [1,] 1 11
> > [2,] 2 12
> > [3,] 3 13
> >
> >
> > And modifying a key column very sensibly makes it no longer a key:
> >
> >
> > > t2 <- data.table(a=1:3,b=1/(1:3),key="a")
> > > key(t2)
> > [1] "a"
> > > t2$a <- 11:13
> > > key(t2)
> > NULL
> >
>
> Yes, all intended and correct, iiuc.
>
> > _______________________________________________
> > datatable-help mailing list
> > datatable-help at lists.r-forge.r-project.org
> >
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>
>
>
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