[R] sum() returns 0 not NA

[(Ted Harding)]

On 20-Apr-10 17:07:31, Joshua Wiley wrote:
> As a disclaimer, I cannot say that this is why sum() was designed as it
> was.
> 
> 0 is the sum of a set with no elements, the empty set {}.  When
> na.rm=TRUE, NA values are removed.  When the only values are NA (as in
> your example c(NA, NA) ), and you remove them all, you are taking the
> sum of no elements, which is 0.
> 
> Also note the behavior of
> 
> sum() # returns 0
> 
> sum is one of the few functions that you can simply call that will not
> return an error.
> 
> HTH,
> 
> Josh
> 
> On Tue, Apr 20, 2010 at 9:42 AM,  <will.eagle at gmx.net> wrote:
>> Dear all,
>>
>> just a stupid R question, since the results puzzle me a bit:
>>
>>> sum(c(NA,NA), na.rm=TRUE)
>> [1] 0
>>> _NA + NA
>> [1] NA
>>> NA + 1
>> [1] NA
>>>
>>
>> Why does sum(c(NA,NA), na.rm=TRUE) return 0 and not NA?
>>
>> Thanks in advance,
>>
>> Will

Exactly the same question was asked, in exactly the same words,
5 days ago:

https://stat.ethz.ch/pipermail/r-help/2010-April/235337.html

and, I suspect, by exactly the same person (thoug using a
different email address). And, also, it was answered 5 days ago.

Was the second sending an accident?
Ted.

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Date: 20-Apr-10                                       Time: 18:24:38
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