From maechler at stat.math.ethz.ch  Wed Aug 26 10:54:27 2015
From: maechler at stat.math.ethz.ch (Martin Maechler)
Date: Wed, 26 Aug 2015 10:54:27 +0200
Subject: [Rd] match()/%in% with language objects?
In-Reply-To: <CAF8bMcbLb1FT2B4umf6jAYAB0hRBViaqA+c7W-XmDn5DrunoBA@mail.gmail.com>
References: <55DC940B.8080701@gmail.com>
	<CAF8bMcbLb1FT2B4umf6jAYAB0hRBViaqA+c7W-XmDn5DrunoBA@mail.gmail.com>
Message-ID: <21981.32451.725608.366953@stat.math.ethz.ch>

>>>>> William Dunlap <wdunlap at tibco.com>
>>>>>     on Tue, 25 Aug 2015 09:47:23 -0700 writes:

    > match(x,table) and x%in%table work when x and table are lists of language
    > objects or expressions.  E.g.,

    > expression(quote(1+2), quote(log2(16))) %in% expression(3, quote(1+2), c(4L,5L,6L,7L))
    > #[1]  TRUE FALSE
    > list(quote(1+2), quote(log2(16))) %in% list(3, quote(1+2), c(4L,5L,6L,7L))
    > #[1]  TRUE FALSE
    > match(list(quote(1+2), quote(log2(16))),  list(3, quote(1+2), c(4L,5L,6L,7L)))
    > #[1]  2 NA

yes, or slightly more naturally for the first case,

 > expression(1+2, log2(16)) %in% expression(3, 1+2, c(4L,5L,6L,7L))
 [1]  TRUE FALSE


    > With your example data:
    > spList[1] %in% spList
    > #[1] TRUE
    > list(quote(foo)) %in% spList
    > #[1] TRUE
    > list(quote(nosuchsymbol)) %in% spList
    > #[1] FALSE

yes  indeed, that works because list()s and expression()s are
"vector"s in the wide sense, as "we all" know.

Did you support Ben's  wish to allow 'symbol' (aka 'name') objects as well,
or even more general language objects (as by the subject's wording) ?

Internally, in these cases the matches do happen with character
coerced objects eventually; still I'd tend to agree that allowing some of
these as arguments to match() in addition to the
wide-sense-vectors (and NULL !) would make sense.

Martin



    > Bill Dunlap
    > TIBCO Software
    > wdunlap tibco.com

    > On Tue, Aug 25, 2015 at 9:12 AM, Ben Bolker <bbolker at gmail.com> wrote:

    >> -----BEGIN PGP SIGNED MESSAGE-----
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    >> 
    >> 
    >> I haven't yet dug into the internals of match() yet to see what's
    >> going on, but I'm wondering whether there's a design reason why I
    >> can't use %in% (which is a wrapper for match()) on language objects.
    >> 
    >> I'd like to test whether a language object is in a list of language
    >> objects, but I get the error "'match' requires vector arguments":
    >> 
    >> specials <- c("foo","bar")
    >> spList <- lapply(specials,as.name)  ## convert to language objects
    >> "a" %in% spList  ## works (FALSE)
    >> spList[[1]] %in% spList ##   'match' requires vector arguments
    >> quote(foo) %in% spList  ## ditto
    >> quote(foo) == spList[[1]]  ## TRUE
    >> 
    >> obviously I can go the other way, converting my target into text:
    >> 
    >> deparse(spList[[1]]) %in% specials  ## TRUE
    >> 
    >> I could also write my own function to loop through the list and stop
    >> when I find it.  But I'd prefer to use built-in functionality if possible.
    >> 
    >> Does anyone have any clues/see what I'm missing?
    >> 
    >> cheers
    >> Ben Bolker
    >> -----BEGIN PGP SIGNATURE-----
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    >> 
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[Rd] match()/%in% with language objects?
Martin Maechler