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

William Dunlap wdunlap at tibco.com
Tue Apr 12 02:37:40 CEST 2016

```Use all.equal instead of identical if you want to gloss over
integer/numeric class differences and minor floating point differences (and
a host of others).

Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Mon, Apr 11, 2016 at 5:25 PM, Paulson, Ariel <apa at stowers.org> wrote:

> Hi Jeff,
>
>
> We are splitting hairs because R is splitting hairs, and causing us
> problems.  Integer and numeric are different R classes with different
> properties, mathematical relationships notwithstanding.  For instance, the
> counterintuitive result:
>
>
> > identical(as.integer(1), as.numeric(1))
> [1] FALSE
>
>
> Unfortunately the reply-to chain doesn't extend far enough -- here is the
> original problem:
>
>
> > sapply(1, identical, 1)
> [1] TRUE
>
> > sapply(1:2, identical, 1)
> [1] FALSE FALSE
>
> > sapply(1:2, function(i) identical(as.numeric(i),1) )
> [1]  TRUE FALSE
>
> > sapply(1:2, function(i) identical(as(i,"numeric"),1) )
> [1] FALSE FALSE
>
> These are the results of R's hair-splitting!
>
> Ariel
>
> ________________________________
> From: Jeff Newmiller <jdnewmil at dcn.davis.ca.us>
> Sent: Monday, April 11, 2016 6:49 PM
> To: Bert Gunter; Paulson, Ariel
> Cc: Rolf Turner; r-help at r-project.org
> Subject: Re: [R] [FORGED] Re: identical() versus sapply()
>
> Hypothesis regarding the thought process: integer is a perfect subset of
> numeric, so why split hairs?
> --
> Sent from my phone. Please excuse my brevity.
>
> On April 11, 2016 12:36:56 PM PDT, Bert Gunter <bgunter.4567 at gmail.com>
> wrote:
>
> 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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>
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>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
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> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

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