On 12/07/2011 12:26 PM, Doran, Harold wrote:
This is just posed out of curiosity, (not as a criticism per se). But what is
the functional role of the argument na.rm inside the mean() function? If there
are missing values, mean() will always return an NA as in the example below.
But, is there ever a purpose in computing a mean only to receive NA as a result?
The general idea in R is that NA stands for "unknown". If some of the
values in a vector are unknown, then the mean of the vector is also
unknown. NA is also used in other ways sometimes; then it makes sense
to remove it and compute the mean of the other values.
Duncan Murdoch
In 10 years of using R, I have always used mean() in order to get a result,
which is the opposite of its default behavior (when there are NAs). Can anyone
suggest a reason why it is in fact desired to get NA as a result of computing
mean()?
> x<- rnorm(100)
> x[1]<- NA
> mean(x)
[1] NA
> mean(x, na.rm=TRUE)
[1] 0.08136736
If the reason is to alert the user that the vector has missing values, I
suppose I could buy that. But, I think other checks are better
Harold
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