[R] zero weights in weighted.mean
Göran Broström
gor@n@bro@trom @end|ng |rom umu@@e
Wed Jul 14 16:46:53 CEST 2021
Den 2021-07-14 kl. 13:16, skrev Duncan Murdoch:
> On 14/07/2021 6:00 a.m., Göran Broström 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,
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