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

[Stefan McKinnon Høj-Edwards]

There is no benefit. It is a rather cumbersome approach to checking whether
something behaves as you expect it to. `as.data.frame` will force it into
what you need; if it cannot be forced, then it will fail. That it can be
converted to a data.frame is the class' designers responsibility, not
yours. So you can use `as.data.frame` on *any* input that you need to
behave as a data.frame.
Consider a grouped tribble; now you have to test 2 different classes.

Kindly,
Stefan

Stefan McKinnon Høj-Edwards
ph.d. Genetics
+44 (0)776 231 2464
+45 2888 6598
Skype: stefan_edwards

2017-09-26 11:15 GMT+01:00 Gábor Csárdi <csardi.gabor at gmail.com>:

> 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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