[Rd] as.list method for by Objects
hpages at fredhutch.org
Tue Jan 30 23:32:16 CET 2018
On 01/30/2018 02:24 PM, Hervé Pagès wrote:
> I agree that it makes sense to expect as.list() to perform
> a "strict coercion" i.e. to return an object of class "list",
> *even* on a list derivative. That's what as( , "list") does
> by default:
> # on a data.frame object
> as(data.frame(), "list") # object of class "list"
> # (but strangely it drops the names)
> # on a by object
> x <- by(warpbreaks[, 1:2], warpbreaks[,"tension"], summary)
> as(x, "list") # object of class "list"
> More generally speaking as() is expected to perform "strict
> coercion" by default, unless called with 'strict=FALSE'.
> That's also what as.list() does on a data.frame:
> as.list(data.frame()) # object of class "list"
> FWIW as.numeric() also performs "strict coercion" on an integer
> as.numeric(1:3) # object of class "numeric"
> So an as.list.env method that does the same as as(x, "list")
oops, I meant as.list.by, sorry...
> would bring a small touch of consistency in an otherwise
> quite inconsistent world of coercion methods(*).
> (*) as(data.frame(), "list", strict=FALSE) doesn't do what you'd
> expect (just one of many examples)
> On 01/29/2018 05:00 PM, Dario Strbenac 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
>>  "by"
>>  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
>> R-devel at r-project.org mailing list
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