[Rd] binary form of is() contradicts its unary form

[Suzen, Mehmet]

Hi Herve,

I think you are confusing subclasses and classes. There is no
contradiction. `is` documentation
is very clear:

`With one argument, returns all the super-classes of this object's class.`

Note that object class is always `data.frame` here, check:

> class(data.frame())
[1] "data.frame"
> is(data.frame(), "data.frame")
[1] TRUE

Best,
Mehmet





On 29 Nov 2017 19:13, "Hervé Pagès" <hpages at fredhutch.org> wrote:

> Hi,
>
> The unary forms of is() and extends() report that data.frame
> extends list, oldClass, and vector:
>
>   > is(data.frame())
>   [1] "data.frame" "list"       "oldClass"   "vector"
>
>   > extends("data.frame")
>   [1] "data.frame" "list"       "oldClass"   "vector"
>
> However, the binary form of is() disagrees:
>
>   > is(data.frame(), "list")
>   [1] FALSE
>   > is(data.frame(), "oldClass")
>   [1] FALSE
>   > is(data.frame(), "vector")
>   [1] FALSE
>
> while the binary form of extends() agrees:
>
>   > extends("data.frame", "list")
>   [1] TRUE
>   > extends("data.frame", "oldClass")
>   [1] TRUE
>   > extends("data.frame", "vector")
>   [1] TRUE
>
> Who is right?
>
> Shouldn't 'is(object, class2)' be equivalent
> to 'class2 %in% is(object)'? Furthermore, is there
> any reason why 'is(object, class2)' is not implemented
> as 'class2 %in% is(object)'?
>
> Thanks,
> H.
>
> --
> Hervé Pagès
>
> Program in Computational Biology
> Division of Public Health Sciences
> Fred Hutchinson Canc
> <https://maps.google.com/?q=Fred+Hutchinson+Canc&entry=gmail&source=g>er
> Research Center
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>
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>
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