R Under development (unstable) (2023-12-09 r85665 ucrt) -- "Unsuffered Consequences"
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> library("matrixStats")
> 
> weightedVar_R <- function(x, w) {
+   mu <- weighted.mean(x, w = w)
+   sum(w * (x - mu) ^ 2) / (sum(w) - 1)
+ }
> 
> 
> n <- 10
> x <- as.double(1:n)
> 
> message("*** weightedVar() ...")
*** weightedVar() ...
> 
> message("- Zero elements")
- Zero elements
> m0 <- var(integer(0))
> m1 <- weightedVar(integer(0), w = integer(0))
> str(list(m0 = m0, m1 = m1))
List of 2
 $ m0: num NA
 $ m1: int NA
> stopifnot(all.equal(m1, m0))
> 
> 
> message("- One elements")
- One elements
> m0 <- var(1)
> m1 <- weightedVar(1)
> str(list(m0 = m0, m1 = m1))
List of 2
 $ m0: num NA
 $ m1: num NA
> stopifnot(all.equal(m1, m0))
> 
> 
> message("- Uniform weights (all w = 1)")
- Uniform weights (all w = 1)
> m0 <- var(x)
> w <- rep(1, times = n)
> m1 <- weightedVar(x, w = w)
> str(list(m0 = m0, m1 = m1))
List of 2
 $ m0: num 9.17
 $ m1: num 9.17
> stopifnot(all.equal(m1, m0))
> 
> 
> message("- Uniform weights (all w = 3)")
- Uniform weights (all w = 3)
> m0 <- var(rep(x, each = 3))
> w <- rep(3, times = n)
> m1 <- weightedVar(x, w = w)
> str(list(m0 = m0, m1 = m1))
List of 2
 $ m0: num 8.53
 $ m1: num 8.53
> stopifnot(all.equal(m1, m0))
> 
> 
> message("- Uniform weights on the first five elements")
- Uniform weights on the first five elements
> idxs <- 1:5
> m0 <- var(x[1:5])
> w <- rep(0, times = n)
> w[idxs] <- 1
> m1 <- weightedVar(x, w = w)
> str(list(m0 = m0, m1 = m1))
List of 2
 $ m0: num 2.5
 $ m1: num 2.5
> stopifnot(all.equal(m1, m0))
> 
> 
> message("- Uniform weights on every second elements")
- Uniform weights on every second elements
> idxs <- seq(from = 1, to = n, by = 2)
> m0 <- var(x[idxs])
> w <- rep(0, times = n)
> w[idxs] <- 1
> m1 <- weightedVar(x, w = w)
> str(list(m0 = m0, m1 = m1))
List of 2
 $ m0: num 10
 $ m1: num 10
> stopifnot(all.equal(m1, m0))
> 
> 
> message("- All weights are zero")
- All weights are zero
> idxs <- integer(0L)
> m0 <- var(x[idxs])
> w <- rep(0, times = n)
> w[idxs] <- 1
> m1 <- weightedVar(x, w = w)
> str(list(m0 = m0, m1 = m1))
List of 2
 $ m0: num NA
 $ m1: num NA
> stopifnot(all.equal(m1, m0))
> 
> message("- Infinite weight on first element")
- Infinite weight on first element
> idxs <- 1L
> m0 <- var(x[idxs])
> w <- rep(0, times = n)
> w[idxs] <- Inf
> m1 <- weightedVar(x, w = w)
> str(list(m0 = m0, m1 = m1))
List of 2
 $ m0: num NA
 $ m1: num NA
> stopifnot(all.equal(m1, m0))
> 
> message("- Missing-value weight on first element")
- Missing-value weight on first element
> idxs <- 1L
> w <- rep(1, times = n)
> w[idxs] <- NA_real_
> m1 <- weightedVar(x, w = w)
> str(list(m1 = m1))
List of 1
 $ m1: num NA
> stopifnot(identical(m1, NA_real_))
> 
> 
> message("- Frequency weights")
- Frequency weights
> 
> ## From https://en.wikipedia.org/wiki/Weighted_arithmetic_mean
> y <-  c(2, 2, 4, 5, 5, 5)
> x <- unique(y)
> w <- table(y)
> stopifnot(names(w) == x)
> 
> m0 <- weightedVar(x, w = w)
> m1 <- var(y)
> stopifnot(all.equal(m1, m0))
> m2 <- weightedVar(x, w = w)
> str(list(m0 = m0, m1 = m1, m2 = m2))
List of 3
 $ m0: num 2.17
 $ m1: num 2.17
 $ m2: num 2.17
> stopifnot(all.equal(m2, m0))
> 
> ## From https://github.com/HenrikBengtsson/matrixStats/issues/72
> large <- c(21, 8, 26, 1, 15, 33, 12, 25, 0, 84)
> years <- c(41706, 9301, 33678, 3082, 27040, 44188, 10049, 30591, 2275, 109831)
> 
> m0 <- weightedVar(large, w = years)
> m1 <- weightedVar(large, w = years)
> str(list(m0 = m0, m1 = m1))
List of 2
 $ m0: num 899
 $ m1: num 899
> stopifnot(all.equal(m1, m0))
> 
> message("*** weightedVar() ... DONE")
*** weightedVar() ... DONE
> 
> proc.time()
   user  system elapsed 
   0.14    0.04    0.17