[Rd] `[` not recognized as a primitive in certain cases.

[Martin Maechler]

>>>>> Joris Meys <jorismeys at gmail.com>
>>>>>     on Tue, 28 Mar 2017 15:19:14 +0200 writes:

    > Thank you gents, I overlooked the subtle differences.

    > On Tue, Mar 28, 2017 at 2:49 PM, Lukas Stadler <lukas.stadler at oracle.com>
    > wrote:

    >> “typeof” is your friend here:
    >> 
    >> > typeof(`[`)
    >> [1] "special"
    >> > typeof(mc[[1]])
    >> [1] "symbol"
    >> > typeof(mc2[[1]])
    >> [1] "special"
    >> 
    >> so mc[[1]] is a symbol, and thus not a primitive.

or  str()  which should be better known to Joe Average useR

> mc <- call("[",iris,2,"Species")
> str(mc[[1]])
 symbol [
> str(`[`)
.Primitive("[") 
> 


    >> - Lukas
    >> 
    >> > On 28 Mar 2017, at 14:46, Michael Lawrence <lawrence.michael at gene.com>
    >> wrote:
    >> >
    >> > There is a difference between the symbol and the function (primitive
    >> > or closure) to which it is bound.
    >> >
    >> > This:
    >> > mc2 <- as.call(list(`[`,iris,2,"Species"))
    >> >
    >> > Evaluates `[` to its value, in this case the primitive object, and the
    >> > primitive itself is incorporated into the returned call.
    >> >
    >> > If you were to do this:
    >> > mc2 <- as.call(list(quote(`[`),iris,2,"Species"))
    >> >
    >> > The `[` would _not_ be evaluated, quote() would return the symbol, and
    >> > the symbol would end up in the call.
    >> >
    >> > The two forms have virtually identical behavior as long as the call
    >> > ends up getting evaluated in the same environment.
    >> >
    >> > On Tue, Mar 28, 2017 at 3:03 AM, Joris Meys <jorismeys at gmail.com> wrote:
    >> >> Dear,
    >> >>
    >> >> I have noticed this problem while looking at the following question on
    >> >> Stackoverflow :
    >> >>
    >> >> http://stackoverflow.com/questions/42894213/s4-class-
    >> subset-inheritance-with-additional-arguments
    >> >>
    >> >> While going through callNextMethod, I've noticed the following odd
    >> >> behaviour:
    >> >>
    >> >> mc <- call("[",iris,2,"Species")
    >> >>
    >> >> mc[[1]]
    >> >> ## `[`
    >> >>
    >> >> is.primitive(`[`)
    >> >> ## [1] TRUE
    >> >>
    >> >> is.primitive(mc[[1]])
    >> >> ## [1] FALSE
    >> >> # Expected to be TRUE
    >> >>
    >> >> mc2 <- as.call(list(`[`,iris,2,"Species"))
    >> >>
    >> >> is.primitive(mc2[[1]])
    >> >> ## [1] TRUE
    >> >>
    >> >> So depending on how I construct the call (using call() or as.call() ),
    >> the
    >> >> function `[` is or is not recognized as a primitive by is.primitive()
    >> >>
    >> >> The behaviour is counterintuitive and -unless I miss something obvious
    >> >> here- likely to be a bug imho. I immediately admit that my C chops
    >> aren't
    >> >> sufficient to come up with a patch.
    >> >>
    >> >> Cheers
    >> >> Joris
    >> >>
    >> >> --
    >> >> Joris Meys
    >> >> Statistical consultant
    >> >>
    >> >> Ghent University
    >> >> Faculty of Bioscience Engineering
    >> >> Department of Mathematical Modelling, Statistics and Bio-Informatics
    >> >>
    >> >> tel :  +32 (0)9 264 61 79
    >> >> Joris.Meys at Ugent.be
    >> >> -------------------------------
    >> >> Disclaimer : http://helpdesk.ugent.be/e-maildisclaimer.php
    >> >>
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    >> >>
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    >> >
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    >> 
    >> 


    > -- 
    > Joris Meys
    > Statistical consultant

    > Ghent University
    > Faculty of Bioscience Engineering
    > Department of Mathematical Modelling, Statistics and Bio-Informatics

    > tel :  +32 (0)9 264 61 79
    > Joris.Meys at Ugent.be
    > -------------------------------
    > Disclaimer : http://helpdesk.ugent.be/e-maildisclaimer.php

    > [[alternative HTML version deleted]]

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