From maechler at stat.math.ethz.ch  Thu Feb  1 16:37:05 2018
From: maechler at stat.math.ethz.ch (Martin Maechler)
Date: Thu, 1 Feb 2018 16:37:05 +0100
Subject: [Rd] as.list method for by Objects
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Message-ID: <23155.13345.961232.702014@stat.math.ethz.ch>

>>>>> Michael Lawrence <lawrence.michael at gene.com>
>>>>>     on Thu, 1 Feb 2018 06:12:20 -0800 writes:

    > On Thu, Feb 1, 2018 at 1:21 AM, Martin Maechler <maechler at stat.math.ethz.ch>
    > wrote:

    >> >>>>> Michael Lawrence <lawrence.michael at gene.com>
    >> >>>>>     on Tue, 30 Jan 2018 10:37:38 -0800 writes:
    >> 
    >> > I agree that it would make sense for the object to have c("by",
    >> "list") as
    >> > its class attribute, since the object is known to behave as a list.
    >> 
    >> Well, but that (list behavior) applies to most non-simple S3
    >> classed objects, say "data.frame", say "lm" to start with real basic ones.
    >> 
    >> The later part of the discussion, seems more relevant to me.
    >> Adding "list" to the class attribute seems as wrong to me as
    >> e.g. adding "double" to "Date" or "POSIXct" (and many more such cases).
    >> 
    >> 
    > There's a distinction though. Date and POSIXct should not really behave as
    > double values (an implementation detail), but "by" is expected to behave as
    > a list (when it is one).

yes, you are right....  As I'm "never"(*) using by(), I'm glad
to leave this issue to you.

Martin

---
*) Never .... [James Bond, 1983]

    > For the present case, we should stay with focusing on  is.list()
    >> being true after as.list() .. the same we would do with
    >> as.numeric() and is.numeric().
    >> 
    >> Martin
    >> 
    >> > However, it would may be too disruptive to make this change at this
    >> point.
    >> > Hard to predict.
    >> 
    >> > Michael
    >> 
    >> > On Mon, Jan 29, 2018 at 5:00 PM, Dario Strbenac <
    >> dstr7320 at uni.sydney.edu.au>
    >> > wrote:
    >> 
    >> >> Good day,
    >> >>
    >> >> I'd like to suggest the addition of an as.list method for a by
    >> object that
    >> >> actually returns a list of class "list". This would make it safer
    >> to do
    >> >> type-checking, because is.list also returns TRUE for a data.frame
    >> variable
    >> >> and using class(result) == "list" is an alternative that only
    >> returns TRUE
    >> >> for lists. It's also confusing initially that
    >> >>
    >> >> > class(x)
    >> >> [1] "by"
    >> >> > is.list(x)
    >> >> [1] TRUE
    >> >>
    >> >> since there's no explicit class definition for "by" and no mention
    >> if it
    >> >> has any superclasses.
    >> >>
    >> >> --------------------------------------
    >> >> Dario Strbenac
    >> >> University of Sydney
    >> >> Camperdown NSW 2050
    >> >> Australia
    >> >>
    >> >> ______________________________________________
    >> >> R-devel at r-project.org mailing list
    >> >> https://stat.ethz.ch/mailman/listinfo/r-devel
    >> >>
    >> >>
    >> 
    >> > [[alternative HTML version deleted]]
    >> 
    >> > ______________________________________________
    >> > R-devel at r-project.org mailing list
    >> > https://stat.ethz.ch/mailman/listinfo/r-devel
    >> 
    >> 

    > [[alternative HTML version deleted]]



[Rd] as.list method for by Objects
Martin Maechler