On 02/01/2016 07:33 AM, Duncan Murdoch wrote:
On 01/02/2016 10:00 AM, Erik Wright wrote:
Dear Frank,
Thank you for the quick response.
I am familiar with the tradeoffs between integers and doubles.
However, I do not believe this answers my question.
If you look at the help information for the as() function it says:
"as(x, "numeric") uses the existing as.numeric function." But clearly
the result is different in each case.
Since is.numeric(1:10) and is(1:10, "numeric") are both true, the as()
function eventually bails out and does nothing.
But it should. Because as() has an extra argument 'strict' that is TRUE
by default. From the man page for as():
strict: logical flag. If ‘TRUE’, the returned object must be
strictly from the target class (unless that class is a
virtual class, in which case the object will be from the
closest actual class, in particular the original object, if
that class extends the virtual class directly).
If ‘strict = FALSE’, any simple extension of the target class
will be returned, without further change. A simple extension
is, roughly, one that just adds slots to an existing class.
So the current behavior is clearly a bug, has been reported several
times, and is known from the R-core folks:
https://stat.ethz.ch/pipermail/r-devel/2015-December/072079.html
FWIW this bug is actually related to this other bug:
x <- 1:10
class(x)
# [1] "integer"
class(x) <- "numeric"
class(x)
# [1] "integer"
Cheers,
H.
So yes, as(x,
"numeric") uses as.numeric() when it needs to coerce, but not when no
coercion is necessary. The docs could perhaps add this condition.
Duncan Murdovh
If the help for as() is correct, then as(1:10, "numeric") should also
return doubles, and the second argument is not ignored.
Erik
> On Feb 1, 2016, at 8:16 AM, Franklin Bretschneider
<brets...@xs4all.nl> wrote:
>
> Dear Erik Wright,
>
>
> Re:
>
>> Could someone please explain this R behavior to me:
>>
>>> typeof(as.numeric(1:10))
>> [1] "double"
>>> typeof(as(1:10, "numeric"))
>> [1] "integer"
>>
>> I expected "double" in both cases. In the help for the "as"
function it says:
>>
>> "Methods are pre-defined for coercing any object to one of the
basic datatypes. For example, as(x, "numeric") uses the existing
as.numeric function."
>
>
> This happens because 1:10 yields only integers, and so can be stored
cheap,
> whereas as.numeric() actually means: as.double.
> The "numeric" in the second line is an unused argument.
>
> Best regards,
>
> Frank
> ---
>
>
>
>
> Franklin Bretschneider
> Dept of Biology
> Utrecht University
> brets...@xs4all.nl
>
>
>
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