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

[Daniel Lüdecke]

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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