[R] is.na behavior

[David Winsemius]

> On Nov 18, 2015, at 5:54 PM, Richard M. Heiberger <rmh at temple.edu> wrote:
> 
> What is the rationale for the following warning in R-3.2.2?
> 
>> is.na(expression(abcd))
> [1] FALSE
> Warning message:
> In is.na(expression(abcd)) :
>  is.na() applied to non-(list or vector) of type ‘expression’

Well, the R interpreter does think that this is not a list:

> is.list(expression(abcd))
[1] FALSE


> methods(is.na)
 [1] is.na,abIndex-method       is.na,denseMatrix-method  
 [3] is.na,indMatrix-method     is.na,nsparseMatrix-method
 [5] is.na,nsparseVector-method is.na,sparseMatrix-method 
 [7] is.na,sparseVector-method  is.na.coxph.penalty*      
 [9] is.na.data.frame           is.na.numeric_version     
[11] is.na.POSIXlt              is.na.raster*             
[13] is.na.ratetable*           is.na.Surv 


So the rationale is probably the same as the rationale for this warning:

> is.na(call("mean", 1:4))
[1] FALSE FALSE
Warning message:
In is.na(call("mean", 1:4)) :
  is.na() applied to non-(list or vector) of type ‘language'

> 	[[alternative HTML version deleted]]


I’m somewhat puzzled at your use of HTML for an Rhelp posting. I thought you were a longtime R user?

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David Winsemius
Alameda, CA, USA