[R-pkg-devel] tibbles are not data frames

[David Hugh-Jones]

These replies seem to be missing the point, which is that old code has to
be rewritten because tibbles don't behave like data frames.

It is true that subclasses can override behaviour, but there is an implicit
contract that the same methods should do the same things.

The as.xxx pattern seems weird to me, though I see it a lot. What is the
point of inheritance if you always have to convert an object upwards before
you can treat it as a member of the superclass?

I can see this argument will run...

David

On 26 September 2017 at 11:15, Gábor Csárdi <csardi.gabor at gmail.com> wrote:

> What is the benefit here, compared to just calling as.data.frame() on it?
>
> Gabor
>
> On Tue, Sep 26, 2017 at 11:11 AM, Daniel Lüdecke <d.luedecke at uke.de>
> wrote:
> > Since tibbles add their class attributes first, you could use:
> >
> > tb <- tibble(a = 5)
> > inherits(tb, "data.frame", which = TRUE) == 1
> >
> > if "tb" is a data frame (only), TRUE is returned, for tibble FALSE. You
> could then coerce to data frame: as.data.frame(tb)
> >
> > -----Ursprüngliche Nachricht-----
> > Von: R-package-devel [mailto:r-package-devel-bounces at r-project.org] Im
> Auftrag von Göran Broström
> > Gesendet: Dienstag, 26. September 2017 12:09
> > An: r-package-devel at r-project.org
> > Betreff: Re: [R-pkg-devel] tibbles are not data frames
> >
> >
> >
> > On 2017-09-26 11:56, Gábor Csárdi wrote:
> >> On Tue, Sep 26, 2017 at 10:35 AM, Joris Meys <Joris.Meys at ugent.be>
> wrote:
> >>> I don't like the dropping of dimensions either. That doesn't change
> >>> the fact that a tibble reacts different from a data.frame. So tibbles
> >>> do not inherit correctly from the class data.frame, and it can thus
> >>> be argued that it's against OOP paradigms to pretend tibbles inherit
> >>> from the class data.frame.
> >>
> >> I have yet to see an OOP system in which a subclass cannot override
> >> the methods of its superclass. Not only is this in line with OOP
> >> paradigms, it is actually one of the essential OOP features.
> >>
> >> To be more constructive, if you have a function that only works with
> >> data frame inputs, then it is good practice to check that the supplied
> >> input is indeed a data frame. This is independent of tibbles.
> >
> > It is not. I check input for being a data frame, but tibbles pass that
> test. That's the essence of the problem.
> >
> >> In practice it seems to me that an easy fix is to just call
> >> as.data.frame on the input. This should either convert it to a data
> >> frame, or throw an error.
> >
> > Sure, but I still need to rewrite the package.
> >
> > Görn
> >
> >> For tibbles it
> >> drops the tbl* classes.
> >>
> >> Gabor
> >>
> >>> Defensive coding techniques would check if it's a tibble and return
> >>> an error saying a data.frame is expected. Unless tibbles inherit
> >>> correctly from data.frame.
> >>>
> >>> I have nothing against tibbles. But calling them "data.frame" raises
> >>> expectations that can't be fulfilled.
> >>
> >> [...]
> >>
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> >>
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