[R] Sum of columns of a data frame equal to NA when all the elements are NA

[peter dalgaard]

No. The empty sum is zero. Adding it to another sum should not change it. Nothing audacious about that. This is consistent; other definitions just cause trouble.

-pd

> On 21 Mar 2018, at 18:05 , Boris Steipe <boris.steipe at utoronto.ca> wrote:
> 
> Surely the result of summation of non-existent values is not defined, is it not? And since the NA values have been _removed_, there's nothing left to sum over. In fact, pretending the the result in that case is zero would appear audacious, no?
> 
> Cheers,
> Boris 
> 
> 
> 
> 
> 
>> On Mar 21, 2018, at 12:58 PM, Jeff Newmiller <jdnewmil at 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.
>> -- 
>> Sent from my phone. Please excuse my brevity.
>> 
>> On March 21, 2018 9:03:29 AM PDT, Boris Steipe <boris.steipe at 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.sofia at 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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-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Office: A 4.23
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com