[R] sum() with na.rm=TRUE, again

[Liaw, Andy]

After stripping NAs, you have a vector of 0 elements.  Sum of such vector is
0, not NA.  Try:

  sum(numeric(0))

Andy

> -----Original Message-----
> From: Richards, Tom [mailto:richards at upci.pitt.edu]
> Sent: Thursday, April 25, 2002 11:26 AM
> To: r-help at stat.math.ethz.ch
> Subject: [R] sum() with na.rm=TRUE, again
> 
> 
> Hi:
> 
> 	I remember a post several days ago by Jon Baron, concerning the
> behavior of sum() when one sets na.rm=TRUE:
> the result will be a zero sum for a vector of all NA's, as 
> here, for the
> second row:
> 
> > ss<- data.frame(x=c(1,NA,3,4),y=c(2,NA,4,NA))
> > ss
>    x  y
> 1  1  2
> 2 NA NA
> 3  3  4
> 4  4 NA
> 
> > apply(ss,1,sum,na.rm=TRUE)
> 1 2 3 4 
> 3 0 7 4 
> 
> I am rather alarmed by that zero, because I was just about to 
> place the sum
> function into am apply() on a rather large data management 
> project, where
> about 5% of my matrix rows have two missing values.  Is there 
> a "safe" way
> to use sum(), so that such zeroes are not created?  A 
> safe.sum() that takes
> arguments just as general as sum()?  I mean, I think I could 
> get around this
> little problem like this,
> 
> apply(ss,1,function(x){ifelse(all(is.na(x)),NA,sum(!is.na(x))*
> mean(x,na.rm=T
> RUE))})
>  1  2  3  4 
>  3 NA  7  4 
> 
> but is there a safer way to write a sum() function?  Or, do 
> these zeroes
> serve some purpose that I am missing?
> Thanks in advance...
> 
> Tom
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