[Rd] oddity in transform

[Gabor Grothendieck]

The idea is that one wants to write the line of code below
 in a general way which works the same
whether you specify ix as one column or multiple columns but the naming entirely
changes when you do this and BOD[, 1] and transform(BOD, X=..., Y=...) or
other hard coding solutions still require writing multiple cases.

ix <- 1:2
transform(BOD, X = BOD[ix] * seq(6))



On Tue, Jul 24, 2018 at 7:14 AM, Emil Bode <emil.bode using dans.knaw.nl> wrote:
> I think you meant to call BOD[,1]
> From ?transform, the ... arguments are supposed to be vectors, and BOD[1] is still a data.frame (with one column). So I don't think it's surprising transform gets confused by which name to use (X, or Time?), and kind of compromises on the name "Time". It's also in a note in ?transform: "If some of the values are not vectors of the appropriate length, you deserve whatever you get!"
> And if you want to do it with multiple extra columns (and are not satisfied with these labels), I think the proper way to go would be " transform(BOD, X=BOD[,1]*seq(6), Y=BOD[,2]*seq(6))"
>
> If you want to trace it back further, it's not in transform but in data.frame. Column-names are prepended with a higher-level name if the object has more than one column.
> And it uses the tag-name if simply supplied with a vector:
> data.frame(BOD[1:2], X=BOD[1]*seq(6)) takes the name of the only column of BOD[1], Time. Only because that column name is already present, it's changed to Time.1
> data.frame(BOD[1:2], X=BOD[,1]*seq(6)) gives third column-name X (as X is now a vector)
> data.frame(BOD[1:2], X=BOD[1:2]*seq(6)) or with BOD[,1:2] gives columns names X.Time and X.demand, to show these (multiple) columns are coming from X
>
> So I don't think there's much to fix here. I this case having X.Time in all cases would have been better, but in general the column-naming of data.frame works, changing it would likely cause a lot of problems.
> You can always change the column-names later.
>
> Best regards,
> Emil Bode
>
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> On 23/07/2018, 16:52, "R-devel on behalf of Gabor Grothendieck" <r-devel-bounces using r-project.org on behalf of ggrothendieck using gmail.com> wrote:
>
>     Note the inconsistency in the names in these two examples.  X.Time in
>     the first case and Time.1 in the second case.
>
>       > transform(BOD, X = BOD[1:2] * seq(6))
>         Time demand X.Time X.demand
>       1    1    8.3      1      8.3
>       2    2   10.3      4     20.6
>       3    3   19.0      9     57.0
>       4    4   16.0     16     64.0
>       5    5   15.6     25     78.0
>       6    7   19.8     42    118.8
>
>       > transform(BOD, X = BOD[1] * seq(6))
>         Time demand Time.1
>       1    1    8.3      1
>       2    2   10.3      4
>       3    3   19.0      9
>       4    4   16.0     16
>       5    5   15.6     25
>       6    7   19.8     42
>
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