Hervé Pagès
2010-Mar-31 22:52 UTC
[Rd] as(1:4, "numeric") versus as.numeric(1:4, "numeric")
Hi, > class(as(1:4, "numeric")) [1] "integer" Surprising but an explanation could be that an integer vector being a particular case of numeric vector, this coercion has nothing to do because 1:4 is already numeric. And indeed: > is.numeric(1:4) [1] TRUE > is.numeric(as(1:4, "numeric")) [1] TRUE However, 'as(1:4, "numeric")' is inconsistent with > class(as.numeric(1:4)) [1] "numeric" And, even more confusing, if you look at the coerce,ANY,numeric method: > selectMethod("coerce", c("integer", "numeric")) Method Definition: function (from, to, strict = TRUE) { value <- as.numeric(from) if (strict) attributes(value) <- NULL value } <environment: namespace:methods> Signatures: from to target "integer" "numeric" defined "ANY" "numeric" it calls as.numeric()! So how can 'as(1:4, "numeric")' not return the same thing as 'as.numeric(1:4)' looks like a mystery to me. Could it be conceivable that I found a bug? Cheers, H. > sessionInfo() R version 2.11.0 Under development (unstable) (2010-03-15 r51282) x86_64-unknown-linux-gnu locale: [1] LC_CTYPE=en_CA.UTF-8 LC_NUMERIC=C [3] LC_TIME=en_CA.UTF-8 LC_COLLATE=en_CA.UTF-8 [5] LC_MONETARY=C LC_MESSAGES=en_CA.UTF-8 [7] LC_PAPER=en_CA.UTF-8 LC_NAME=C [9] LC_ADDRESS=C LC_TELEPHONE=C [11] LC_MEASUREMENT=en_CA.UTF-8 LC_IDENTIFICATION=C attached base packages: [1] stats graphics grDevices utils datasets methods base -- Herv? Pag?s Program in Computational Biology Division of Public Health Sciences Fred Hutchinson Cancer Research Center 1100 Fairview Ave. N, M2-B876 P.O. Box 19024 Seattle, WA 98109-1024 E-mail: hpages at fhcrc.org Phone: (206) 667-5791 Fax: (206) 667-1319
John Chambers
2010-Mar-31 23:52 UTC
[Rd] as(1:4, "numeric") versus as.numeric(1:4, "numeric")
The example is confusing and debatable, but not an obvious bug. And your presentation of it is the cause of much of the confusion (unintentionally I'm sure). First, slipping from the as() function to methods for the coerce() function might surprise a less experienced user. And in fact, that is the point here. If you look at the as() function, it jumps through several hoops and in particular selects a method from coerce in such a way as NOT to use inheritance on the from= argument. (I think this makes sense in this case). So I would assert that your selectMethod() output below came from a different session than the as(1:4, "numeric"). Starting from a clean session with R 2.10.1: > class(as(1:4,"numeric")) [1] "integer" > selectMethod("coerce", c("integer","numeric")) Method Definition: function (from, to = "numeric", strict = TRUE) if (strict) { class(from) <- "numeric" from } else from <environment: namespace:methods> Signatures: from to target "integer" "numeric" defined "integer" "numeric" Note, no call to as.numeric(). In a session without a previous call to as(), your selectMethod() call triggered a standard inherited method selection. And if you had then gone on to as(), the result would have been different. In a different clean session: > getMethod("coerce", c("integer", "numeric")) Error in getMethod("coerce", c("integer", "numeric")) : No method found for function "coerce" and signature integer, numeric > selectMethod("coerce", c("integer", "numeric")) Method Definition: function (from, to, strict = TRUE) { value <- as.numeric(from) if (strict) attributes(value) <- NULL value } <environment: namespace:methods> Signatures: from to target "integer" "numeric" defined "ANY" "numeric" > class(as(1:4,"numeric")) [1] "numeric" No argument about this being confusing. Perhaps one should prohibit standard selectMethod() on coerce() but that seems a bit arcane to thwart folks like you! Suggested improvements for the current implementation are welcome, so long as they consider the best definition of as() in the general sense. Regards, John On 3/31/10 3:52 PM, Herv? Pag?s wrote:> Hi, > > > class(as(1:4, "numeric")) > [1] "integer" > > Surprising but an explanation could be that an integer > vector being a particular case of numeric vector, this > coercion has nothing to do because 1:4 is already numeric. > And indeed: > > > is.numeric(1:4) > [1] TRUE > > is.numeric(as(1:4, "numeric")) > [1] TRUE > > However, 'as(1:4, "numeric")' is inconsistent with > > > class(as.numeric(1:4)) > [1] "numeric" > > And, even more confusing, if you look at the coerce,ANY,numeric > method: > > > selectMethod("coerce", c("integer", "numeric")) > Method Definition: > > function (from, to, strict = TRUE) > { > value <- as.numeric(from) > if (strict) > attributes(value) <- NULL > value > } > <environment: namespace:methods> > > Signatures: > from to > target "integer" "numeric" > defined "ANY" "numeric" > > it calls as.numeric()! > > So how can 'as(1:4, "numeric")' not return the same thing as > 'as.numeric(1:4)' looks like a mystery to me. Could it be > conceivable that I found a bug? > > Cheers, > H. > > > > sessionInfo() > R version 2.11.0 Under development (unstable) (2010-03-15 r51282) > x86_64-unknown-linux-gnu > > locale: > [1] LC_CTYPE=en_CA.UTF-8 LC_NUMERIC=C > [3] LC_TIME=en_CA.UTF-8 LC_COLLATE=en_CA.UTF-8 > [5] LC_MONETARY=C LC_MESSAGES=en_CA.UTF-8 > [7] LC_PAPER=en_CA.UTF-8 LC_NAME=C > [9] LC_ADDRESS=C LC_TELEPHONE=C > [11] LC_MEASUREMENT=en_CA.UTF-8 LC_IDENTIFICATION=C > > attached base packages: > [1] stats graphics grDevices utils datasets methods base > >