R 1.8.1 with Windows XP.
I have a question about how sd() behaves with NA's:
> mean(c(1,2,3,NA))
[1] NA
> median(c(1,2,3,NA))
[1] NA
> mad(c(1,2,3,NA))
[1] NA
> sd(c(1,2,3,NA))
Error in var(x, na.rm = na.rm) : missing observations in cov/cor
>
What is so special about the standard deviation, relative to
other descriptive statistics, that the presence of NA's
deserves an error instead of simply returning NA?
(I know about na.rm=TRUE, but that is not the point here.)
A few small changes to sd() would seem to resolve the anomaly:
sd <- function(x, na.rm=FALSE)
# Function like built-in 'sd', but return NA instead of error when
# 'na.rm' is FALSE and 'x' has NA's.
{
if (is.matrix(x)) {
apply(x, 2, sd, na.rm = na.rm)
} else if (is.vector(x)) {
if (!na.rm && any(is.na(x))) NA
else sqrt(var(x, na.rm = na.rm))
} else if (is.data.frame(x)) {
sapply(x, sd, na.rm = na.rm)
} else {
x <- as.vector(x)
if (!na.rm && any(is.na(x))) NA
else sqrt(var(x, na.rm = na.rm))
}
}
Rich Raubertas
Merck & Co.
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