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1.4.0: mean/sum of logicals

3 messages · Torsten Hothorn, Peter Dalgaard, Brian Ripley

Original
Torsten Hothorn
# 
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

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Peter Dalgaard
# 
Torsten Hothorn <Torsten.Hothorn@rzmail.uni-erlangen.de> writes:
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...
Brian Ripley
#
On 5 Oct 2001, Peter Dalgaard BSA wrote:

            

      
      
      
    

        
Back-compatibility.  In data frames logicals used to get coerced to
two-level factors, not to numerics, and then mean would fail for them.
If a logical is an experimental factor, sums make sense but means do not.

Here is what I find confusing (1.3.1).

            

      
      
      
    

        
[1] 0.5

            

      
      
      
    

        
Error in Summary.factor(..., na.rm = na.rm) :
        "sum" not meaningful for factors

There 1.4.0 is consistent.

Change it if you like, but do think through all the implications of the
inconsistent treatment of logicals (for which I have not had time as yet).