It's convention in mathematics that the empty sum is 0. You can think of this as a generalization of 0*x = 0.
Reid Huntsinger -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Denis Chabot Sent: Friday, February 04, 2005 11:01 AM To: r-help@stat.math.ethz.ch Subject: [R] 2 small problems: integer division and the nature of NA 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 ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html