[R] Cannot calculate mean() for double vector

[Reuben Bellika]

It looks like I should read the documentation a bit more carefully.
Simply ignoring the NA values when calculating the mean *is* a much
better solution. (Although having 10 values out of a vector of 40000
or so set to zero is *not* going to bias the mean toward zero in any
significant way.)

Thanks to everyone for your help.

Reuben