I encountered an unexpected difference in the way that mean and var work:
> mean(numeric(0))
[1] NaN
> var(numeric(0))
Error in var(numeric(0)) : `x' is empty
Looking into this, I discovered in mean.default that sum(x)/n
evaluates as> sum(numeric(0))/length(numeric(0))
[1] NaN
The function var calls an .Internal and seems to evaluate
this:> .Internal(cov(numeric(0),NULL,"all.obs"))
Error: `x' is empty
Best,
Kevin Wright, Research Scientist
Pioneer Hi-Bred Int'l, x4054.
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