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

[Boris Steipe]

I see: consistency with additive identity. That makes sense. Thanks.

B.


> On Mar 21, 2018, at 1:22 PM, peter dalgaard <pdalgd at gmail.com> wrote:
> 
> 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
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