> On Mar 21, 2018, at 9:58 AM, Jeff Newmiller <jdnew...@dcn.davis.ca.us> wrote:
>
> What do you mean by "should not"?
>
> NULL means "missing object" in R. The result of the sum function is always
> expected to be numeric... so NA_real or NA_integer could make sense as
> possible return values. But you cannot compute on NULL so no, that doesn't
> work.
>
> See the note under the "Value" section of ?sum as to why zero is returned
> when all inputs are removed.
But your perspective above that sentence is at odds with the note in the
Details section of the same document:
> sum(NULL)
[1] 0
> ?sum
starting httpd help server ... done
> sum( integer(0) )
[1] 0
Best;
David
> --
> Sent from my phone. Please excuse my brevity.
>
> On March 21, 2018 9:03:29 AM PDT, Boris Steipe <boris.ste...@utoronto.ca>
> wrote:
>> Should not the result be NULL if you have removed the NA with
>> na.rm=TRUE ?
>>
>> B.
>>
>>
>>
>>> On Mar 21, 2018, at 11:44 AM, Stefano Sofia
>> <stefano.so...@regione.marche.it> wrote:
>>>
>>> Dear list users,
>>> let me ask you this trivial question. I worked on that for a long
>> time, by now.
>>> Suppose to have a data frame with NAs and to sum some columns with
>> rowSums:
>>>
>>> df <- data.frame(A = runif(10), B = runif(10), C = rnorm(10))
>>> df[1, ] <- NA
>>> rowSums(df[ , which(names(df) %in% c("A","B"))], na.rm=T)
>>>
>>> If all the elements of the selected columns are NA, rowSums returns 0
>> while I need NA.
>>> Is there an easy and efficient way to use rowSums within a function
>> like
>>>
>>> function(x) ifelse(all(is.na(x)), as.numeric(NA), rowSums...)?
>>>
>>> or an equivalent function?
>>>
>>> Thank you for your help
>>> Stefano
>>>
>>>
>>>
>>> (oo)
>>> --oOO--( )--OOo----------------
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>> ______________________________________________
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>
> ______________________________________________
> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
David Winsemius
Alameda, CA, USA
'Any technology distinguishable from magic is insufficiently advanced.'
-Gehm's Corollary to Clarke's Third Law
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