From p.dalgaard@biostat.ku.dk  Fri Oct  5 12:44:51 2001
From: p.dalgaard@biostat.ku.dk (Peter Dalgaard BSA)
Date: 05 Oct 2001 13:44:51 +0200
Subject: [Rd] 1.4.0: mean/sum of logicals
In-Reply-To: <Pine.LNX.4.21.0110051314040.12509-100000@artemis.imbe.med.uni-erlangen.de>
References: <Pine.LNX.4.21.0110051314040.12509-100000@artemis.imbe.med.uni-erlangen.de>
Message-ID: <x2itduwbt8.fsf@blueberry.kubism.ku.dk>

Torsten Hothorn <Torsten.Hothorn@rzmail.uni-erlangen.de> writes:

> the NEWS file in  1.4.0-devel states: 
> 
> o   mean() has `data frame' method applying mean column-by-column.
>     When applied to non-numeric data mean() now returns NA rather
>     than a confusing error message (for compatibility with S4).
> 
> 
> which means: 
> 
> R> mean(c(TRUE, FALSE))
> [1] NA
> Warning message: 
> argument is not numeric: returning NA in: mean.default(c(TRUE, FALSE)) 
> 
> but: 
> 
> R> sum(c(TRUE, FALSE))
> [1] 1
> 
> ?sum states: 
> 
>      sum(..., na.rm=FALSE)
> 
> Arguments:
> 
>      ...: numeric vectors.
> 
> and clearly
> 
> R> is.numeric(c(TRUE, FALSE))
> [1] FALSE
> 
> 
> this is confusing, isn't it? I think that `sum' and `mean' should take the
> same arguments (and one probably will not allow to sum up logicals) or am
> I missing something?
> 
> Torsten

Hmm. That slipped in without me noticing. Summing logicals is a fairly
common practice, as in 

sem <- sd(x,na.rm=TRUE)/sqrt(sum(!is.na(x)))

Taking means of logicals is somewhat more rare, but it does work in
Splus 6.0 and it is a general rule coerce to logicals to 0/1, so I
suspect that this is just an oversight and we want mean.default to
start with

    if (!is.numeric(x) && !is.complex(x) && !is.logical(x)) {
        warning("argument is not numeric: returning NA")
        return(as.numeric(NA))

If Brian really meant otherwise, he'll explain why when he gets back
from Switzerland...

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk)             FAX: (+45) 35327907
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-devel mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-devel-request@stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._


[Rd] 1.4.0: mean/sum of logicals
Peter Dalgaard BSA