R devel - Dec 2015 - For integer vectors, `as(x, "numeric")` has no effect.

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")`?

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")`?

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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