This function computes the standard deviation of the values in
TRUE then missing values are removed before
a numeric vector or an R object which is coercible to one
logical. Should missing values be removed?
var this uses denominator n - 1.
The standard deviation of a zero-length vector (after removal of
na.rm = TRUE) is not defined and gives an error.
The standard deviation of a length-one vector is
var for its square, and
mad, the most
sd(1:2) ^ 2