weighted.mean() yields incorrect result when units are effectively [1]
dholstius opened this issue · 0 comments
dholstius commented
Summary
It seems that when the units on x are effectively [1], as with day/week or lb/ton, then stats::weighted.mean() yields the wrong answer.
Reprex
library(units)
#> Warning: package 'units' was built under R version 4.2.3
#> udunits database from /Library/Frameworks/R.framework/Versions/4.2-arm64/Resources/library/units/share/udunits/udunits2.xml
w <- c(1, 1) # keep it simple
wtd_mean <- function (x, w, ...) {
mu <- sum(x * w, ...) / sum(w, ...)
set_units(mu, units(x), mode = "character")
}
# just to illustrate that `wtd_mean()` does the right thing
# these are all correct
x <- set_units(c(2, 4), "lb/week")
mean(x)
#> 3 [lb/week]
wtd_mean(x, w)
#> 3 [lb/week]
weighted.mean(x, w)
#> 3 [lb/week]
# here, weighted.mean() gets the wrong answer
# note: 0.429 [unitless] would be equivalent to 3/7 [day/week]
x <- set_units(c(2, 4), "day/week")
mean(x)
#> 3 [d/week]
wtd_mean(x, w)
#> 3 [d/week]
weighted.mean(x, w)
#> 0.4285714 [d/week]
# it's not only units of time
x <- set_units(c(2, 4), "lb/ton")
mean(x)
#> 3 [lb/ton]
wtd_mean(x, w)
#> 3 [lb/ton]
weighted.mean(x, w)
#> 0.0015 [lb/ton]Created on 2024-01-10 with reprex v2.0.2
Session info
sessioninfo::session_info()
#> ─ Session info ───────────────────────────────────────────────────────────────
#> setting value
#> version R version 4.2.0 (2022-04-22)
#> os macOS 14.2
#> system aarch64, darwin20
#> ui X11
#> language (EN)
#> collate en_US.UTF-8
#> ctype en_US.UTF-8
#> tz America/Los_Angeles
#> date 2024-01-10
#> pandoc 3.1.1 @ /Applications/RStudio.app/Contents/Resources/app/quarto/bin/tools/ (via rmarkdown)
#>
#> ─ Packages ───────────────────────────────────────────────────────────────────
#> package * version date (UTC) lib source
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#> yaml 2.3.8 2023-12-11 [1] CRAN (R 4.2.3)
#>
#> [1] /Library/Frameworks/R.framework/Versions/4.2-arm64/Resources/library
#>
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