R help - Jul 2021 - zero weights in weighted.mean

On 14/07/2021 6:00 a.m., G?ran Brostr?m wrote:
> I wonder about the last sentence in the Details section of the
> documentation of 'weighted.mean':
> 
> "However, zero weights _are_ handled specially and the corresponding
?x?
> values are omitted from the sum."
> 
> The return value of weighted.mean.default is
> 
> sum((x * w)[w != 0])/sum(w)
> 
> and indeed, it looks as if zero weights are getting special treatment,
> but what is wrong with the alternative (equivalent?) expression
> 
> sum(x * w) / sum(w)?
> 
> Is it a good idea to remove zeros from a vector before applying
'sum' to
> it? I don't think so. Anyway, the sentence in the documentation seems
to
> be uncalled for.
Inf*0 is not zero.  Setting weights to zero on infinite observations (or 
NA, or NaN) will give different results in your two expressions.

Duncan Murdoch

Den 2021-07-14 kl. 13:16, skrev Duncan Murdoch:
> On 14/07/2021 6:00 a.m., G?ran Brostr?m wrote:
>> I wonder about the last sentence in the Details section of the
>> documentation of 'weighted.mean':
>>
>> "However, zero weights _are_ handled specially and the
corresponding ?x?
>> values are omitted from the sum."
>>
>> The return value of weighted.mean.default is
>>
>> sum((x * w)[w != 0])/sum(w)
>>
>> and indeed, it looks as if zero weights are getting special treatment,
>> but what is wrong with the alternative (equivalent?) expression
>>
>> sum(x * w) / sum(w)?
>>
>> Is it a good idea to remove zeros from a vector before applying
'sum' to
>> it? I don't think so. Anyway, the sentence in the documentation
seems to
>> be uncalled for.
> 
> Inf*0 is not zero.? Setting weights to zero on infinite observations (or 
> NA, or NaN) will give different results in your two expressions.
Thanks, agreed.

G,