[Rd] transform

[Gabor Grothendieck]

Suggest you look at dplyr::mutate as this functionality is widely used
there and has shown itself to be useful.

On Tue, Aug 27, 2024 at 9:16 AM Sebastian Meyer <seb.meyer using fau.de> wrote:
>
> Am 27.08.24 um 11:55 schrieb peter dalgaard:
> > Yes. A quirk, rather than a bug I'd say. One issue is that the internal logic of transform() relies on
> >
> >      e <- eval(substitute(list(...)), `_data`, parent.frame())
> >      tags <- names(e)
> >
> > so untagged entries in ... will not be included.
>
> ... unless at least one is tagged:
>
> R> transform(BOD, 0:5, 1:6)
>    Time demand
> 1    1    8.3
> 2    2   10.3
> 3    3   19.0
> 4    4   16.0
> 5    5   15.6
> 6    7   19.8
>
> R> transform(BOD, 0:5, 1:6, foo = 1)
>    Time demand 0:5 1:6 foo
> 1    1    8.3   0   1   1
> 2    2   10.3   1   2   1
> 3    3   19.0   2   3   1
> 4    4   16.0   3   4   1
> 5    5   15.6   4   5   1
> 6    7   19.8   5   6   1
>
> But as transform.data.frame is only documented for tagged vector
> expressions, all examples provided in this thread were formal misuses.
> (It might make sense to warn about untagged entries.)
>
> Personally, I'd be quite confused about what to expect from syntax like
>
>      transform(BOD, data.frame(y = 1:6))
>
> as really no transformation is specified. Looks like cbind() or
> data.frame() was meant.
>
>         Sebastian
>
>
> > The other part is a direct consequence of a quirk in data.frame:
> >
> >> data.frame(head(airquality), y=data.frame(x=rnorm(6)))
> >    Ozone Solar.R Wind Temp Month Day          x
> > 1    41     190  7.4   67     5   1  0.3075402
> > 2    36     118  8.0   72     5   2  0.7765265
> > 3    12     149 12.6   74     5   3  0.3909341
> > 4    18     313 11.5   62     5   4  0.4733170
> > 5    NA      NA 14.3   56     5   5 -0.6947709
> > 6    28      NA 14.9   66     5   6  0.1126040
> >
> > whereas (the wisdom of this escapes me)
> >
> >> data.frame(head(airquality), y=data.frame(x=rnorm(6),z=rnorm(6)))
> >    Ozone Solar.R Wind Temp Month Day        y.x         y.z
> > 1    41     190  7.4   67     5   1 -0.9250228  0.46483406
> > 2    36     118  8.0   72     5   2 -0.5035793  0.28822668
> > ...
> >
> > On the whole, I think that transform was never designed (nor documented) to take data frame arguments, so caveat emptor.
> >
> > - Peter
> >
> >
> >> On 24 Aug 2024, at 16:41 , Gabor Grothendieck <ggrothendieck using gmail.com> wrote:
> >>
> >> One oddity in transform that I recently noticed.  It seems that to include
> >> a one-column data frame in the arguments one must name it even though the
> >> name is ignored.  If the data frame has more than one column then it must
> >> also be named but in that case it is not ignored and the names are made up of
> >> a combination of that name and the data frame's names.  I would have thought
> >> that if we did not want a combination of names we would just not name the
> >> argument.
> >>
> >>   # ignores second argument returning BOD unchanged
> >>   transform(BOD, data.frame(y = 1:6)) |> names()
> >>   ## [1] "Time"   "demand"
> >>
> >>   # ignores second argument returning BOD unchanged
> >>   transform(BOD, data.frame(y = 1:6, z = 6:1)) |> names()
> >>   ## [1] "Time"   "demand"
> >>
> >>   # with one column in data frame it adds the column and names it y ignoring x
> >>   transform(BOD, x = data.frame(y = 1:6)) |> names()
> >>   ## [1] "Time"   "demand" "y"
> >>
> >>   # with multiple columns in data frame it uses x.y and x.z as names
> >>   transform(BOD, data.frame(y = 1:6, z = 6:1)) |> names()
> >>   ## [1] "Time"   "demand" "x.y"    "x.z"
> >>
> >>
> >> --
> >> Statistics & Software Consulting
> >> GKX Group, GKX Associates Inc.
> >> tel: 1-877-GKX-GROUP
> >> email: ggrothendieck at gmail.com
> >>
> >> ______________________________________________
> >> R-devel using r-project.org mailing list
> >> https://stat.ethz.ch/mailman/listinfo/r-devel
> >



-- 
Statistics & Software Consulting
GKX Group, GKX Associates Inc.
tel: 1-877-GKX-GROUP
email: ggrothendieck at gmail.com