From p.dalgaard at biostat.ku.dk  Wed Jun 20 18:37:15 2007
From: p.dalgaard at biostat.ku.dk (Peter Dalgaard)
Date: Wed, 20 Jun 2007 18:37:15 +0200
Subject: [Rd] Expected behavior from:  all(c(NA, NA, NA) < NA,
 na.rm = TRUE)?
In-Reply-To: <1182354805.3785.47.camel@Bellerophon.localdomain>
References: <1182354805.3785.47.camel@Bellerophon.localdomain>
Message-ID: <467957BB.8010602@biostat.ku.dk>

Marc Schwartz wrote:
> Hi all,
>
> Came across this curious behavior in:
>
>   R version 2.5.0 Patched (2007-06-05 r41831)
>
>
> A simplified example is:
>
>   
>> all(c(NA, NA, NA) > NA, na.rm = TRUE)
>>     
> [1] TRUE
>
>
> Is this expected by definition?
>
> If one reduces this to individual comparisons, such as :
>
>   
>> NA > NA
>>     
> [1] NA
>
>   
>> all(NA > NA)
>>     
> [1] NA
>
>   
>> all(NA > NA, na.rm = TRUE)
>>     
> [1] TRUE
>
> the initial comparison on the 3 element vector would be consistent with
> the last example. 
>
> If one evaluates each side of the comparison within the parens in the
> initial example, you get something along the lines of the following:
>
> x <- c(NA, NA, NA)
> x <- x[!is.na(x)]   # remove NA's (eg. mean.default(x, na.rm = TRUE))
>
>   
>> x
>>     
> logical(0)
>
>   
>> logical(0) > NA
>>     
> logical(0)
>
>   
>> all(logical(0))
>>     
> [1] TRUE
>
>
> If my train of thought is correct, it seems to me that the behavior
> above distills down to the comparison between logical(0) and NA, which
> rather than returning NA, returns logical(0). 
>
> This would seem appropriate, given that there is no actual comparison
> being made with NA, I think, since logical(0) is an 'empty' vector.
>
> However, should all(logical(0)) return TRUE or logical(0)?  For example:
>
>   
>> logical(0) == logical(0)
>>     
> logical(0)
>
>   
>> all(logical(0) == logical(0))
>>     
> [1] TRUE
>
>
> If the initial comparison of logical(0) returns logical(0), which is not
> TRUE:
>
>   
>> logical(0) == TRUE
>>     
> logical(0)
>
> then why does all() return TRUE, if the individual comparison is not
> TRUE?  By definition from ?all:
>
> Given a sequence of logical arguments, a logical value indicating
> whether or not all of the elements of x are TRUE. 
> The value returned is TRUE if all of the values in x are TRUE, and FALSE
> if any of the values in x are FALSE. 
> If na.rm = FALSE and x consists of a mix of TRUE and NA values, the
> value is NA.
>
>
>
> Does this make any sense?
>   
I don't see the problem. Isn't it just that all(logical(0))==TRUE by 
convention just like prod(numeric(0))==1 etc.?



[Rd] Expected behavior from: all(c(NA, NA, NA) < NA, na.rm = TRUE)?
Peter Dalgaard