[R] [FORGED] Re: identical() versus sapply()

[Bert Gunter]

Indeed!

Slightly simplified to emphasize your point:

> class(as(1:2,"numeric"))
[1] "integer"

> class(as.numeric(1:2))
[1] "numeric"

whereas in ?as it says:

"Methods are pre-defined for coercing any object to one of the basic
datatypes. For example, as(x, "numeric") uses the existing as.numeric
function. "

I suspect this is related to my ignorance of S4 classes (i.e. as() )
and how they relate to S3 classes, but I certainly don't get it
either.

Cheers,
Bert



Bert Gunter

"The trouble with having an open mind is that people keep coming along
and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )


On Mon, Apr 11, 2016 at 9:30 AM, Paulson, Ariel <apa at stowers.org> wrote:
> Ok, I see the difference between 1 and 1:2, I'll just leave it as one of those "only in R" things.
>
> But it seems then, that as.numeric() should guarantee a FALSE outcome, yet it does not.
>
> To build on what Rolf pointed out, I would really love for someone to explain this one:
>
>> str(1)
>  num 1
>
>> str(1:2)
>  int [1:2] 1 2
>
>> str(as.numeric(1:2))
>  num [1:2] 1 2
>
>> str(as(1:2,"numeric"))
>  int [1:2] 1 2
>
> Which doubly makes no sense.  1) Either the class is "numeric" or it isn't; I did not call as.integer() here.  2) method of recasting should not affect final class.
>
> Thanks,
> Ariel
>
>
> -----Original Message-----
> From: Rolf Turner [mailto:r.turner at auckland.ac.nz]
> Sent: Saturday, April 09, 2016 5:27 AM
> To: Jeff Newmiller
> Cc: Paulson, Ariel; 'r-help at r-project.org'
> Subject: Re: [FORGED] Re: [R] identical() versus sapply()
>
> On 09/04/16 16:24, Jeff Newmiller wrote:
>> I highly recommend making friends with the str function. Try
>>
>> str( 1 )
>> str( 1:2 )
>
> Interesting.  But to me counter-intuitive.  Since R makes no distinction between scalars and vectors of length 1 (or more accurately I think, since in R there is *no such thing as a scalar*, only a vector of length
> 1) I don't see why "1" should be treated in a manner that is categorically different from the way in which "1:2" is treated.
>
> Can you, or someone else with deep insight into R and its rationale, explain the basis for this difference in treatment?
>
>> for the clue you need, and then
>>
>> sapply( 1:2, identical, 1L )
>
> cheers,
>
> Rolf
>
> --
> Technical Editor ANZJS
> Department of Statistics
> University of Auckland
> Phone: +64-9-373-7599 ext. 88276
>
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