On 2021-07-14 19:43, Sorkin, John wrote:
Gentlemen,
At the risk of beating a dead horse, but in he spirit of learning
more about R, aren't the two expressions functionally the same? One
drops values where weight is zero. The other (in the case where we
and infinity * 0, something one would not expect to see in data) also
drops data as in R infinity * 0 = Nan. In either case the observation
would be dropped. I am certain I am missing something, but I don't
know what I am missing.
Try this:
> my <- function(x, w) sum(x * w) / sum(w)
> x <- c(1, 1 / 0)
> w <- 1:0
> my(x, w)
[1] NaN
> weighted.mean(x, w)
[1] 1
See?
Best, Göran
John
John David Sorkin M.D., Ph.D. Professor of Medicine University of
Maryland School of Medicine Associate Director for Biostatistics and
Informatics Baltimore VA Medical Center Geriatrics, Research,
Education, and Clinical Center Chief, Biostatistics and Informatics
University of Maryland School of Medicine Division of Gerontology,
Geriatrics and Palliative Care Senior Statistician University of
Maryland Center for Vascular Research 10 North Greene Street GRECC
(BT/18/GR) Baltimore, MD 21201-1524 (Phone) 410-605-7119 (Fax)
410-605-7913 (Please call phone number above prior to faxing)
________________________________________ From: R-help
<r-help-boun...@r-project.org> on behalf of Göran Broström
<goran.brost...@umu.se> Sent: Wednesday, July 14, 2021 10:46 AM To:
Duncan Murdoch; r-help@r-project.org Subject: Re: [R] zero weights in
weighted.mean
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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