From jmc at r-project.org  Tue Dec  8 01:05:59 2015
From: jmc at r-project.org (John Chambers)
Date: Mon, 7 Dec 2015 16:05:59 -0800
Subject: [Rd] For integer vectors, `as(x, "numeric")` has no effect.
In-Reply-To: <56661824.9020707@gmail.com>
References: <CAOwKfPTq9TZaV6j9KxbpFuDpZdyskDB9egL7B911QP3oaR6vOw@mail.gmail.com>
	<56661824.9020707@gmail.com>
Message-ID: <16F6D0AF-6667-45CF-9CBF-6BC19D514951@r-project.org>

We do need an explicit method here, I think.

The issue is that as() uses methods for the generic function coerce() but cannot use inheritance in the usual way (if it did, you would be immediately back with no change, since "integer" inherits from "numeric").

Copying in the general method for coercing to "numeric" as an explicit method for "integer" gives the expected result:

> setMethod("coerce", c("integer", "numeric"), getMethod("coerce", c("ANY", "numeric")))
[1] "coerce"
> typeof(as(1L, "numeric"))
[1] "double"

Seems like a reasonable addition to the code, unless someone sees a problem.

John


On Dec 7, 2015, at 3:37 PM, Benjamin Tyner <btyner at gmail.com> wrote:

> Perhaps it is not that surprising, given that
> 
>    > mode(1L)
>    [1] "numeric"
> 
> and
> 
>    > is.numeric(1L)
>    [1] TRUE
> 
> On the other hand, this is curious, to say the least:
> 
>    > is.double(as(1L, "double"))
>    [1] FALSE
> 
>> Here's the surprising behavior:
>> 
>>    x <- 1L
>>    xx <- as(x, "numeric")
>>    class(xx)
>>    ## [1] "integer"
>> 
>> It occurs because the call to `as(x, "numeric")` dispatches the coerce
>> S4 method for the signature `c("integer", "numeric")`, whose body is
>> copied in below.
>> 
>>     function (from, to = "numeric", strict = TRUE)
>>     if (strict) {
>>         class(from) <- "numeric"
>>         from
>>     } else from
>> 
>> This in turn does nothing, even when strict=TRUE, because that
>> assignment to class "numeric" has no effect:
>> 
>>     x <- 10L
>>     class(x) <- "numeric"
>>     class(x)
>>     [1] "integer"
>> 
>> Is this the desired behavior for `as(x, "numeric")`?
> 
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[Rd] For integer vectors, `as(x, "numeric")` has no effect.
John Chambers