[R] 2 small problems: integer division and the nature of NA

[Denis Chabot]

Hi,

I'm wondering why

48 %/% 2 gives 24
but
4.8 %/% 0.2 gives 23...
I'm not trying to round up here, but to find out how many times 
something fits into something else, and the answer should have been the 
same for both examples, no?

On a different topic, I like the behavior of NAs better in R than in 
SAS (at least they are not considered the smallest value for a 
variable), but at the same time I am surprised that the sum of NAs is 0 
instead of NA.

The sum of a vector having at least one NA but also valid data gives NA 
if we do not specify na.rm=T. But with na.rm=T, we are telling sum to 
give the sum of valid data, ignoring NAs that do not tell us anything 
about the value of a variable. I found out while getting the sum of 
small subsets of my data (such as when subsetting by several 
variables), sometimes a "cell" only contained NAs for my response 
variable. I would have expected the sum to be NA in such cases, as I do 
not have a single data point telling me the value of my response here. 
But R tells me the sum was zero in that cell! Was this behavior 
considered "desirable" when sum was built? If not, any hope it will be 
fixed?

Sincerely,

Denis Chabot