Hello, R friends My student unearthed this quirk that might interest you.
I wondered if this might be a bug in the R interpreter. If not a bug, it certainly stands as a good example of the dangers of floating point numbers in computing. What do you think? > 100*(23/40) [1] 57.5 > (100*23)/40 [1] 57.5 > round(100*(23/40)) [1] 57 > round((100*23)/40) [1] 58 The result in the 2 rounds should be the same, I think. Clearly some digital number devil is at work. I *guess* that when you put in whole numbers and group them like this (100*23), the interpreter does integer math, but if you group (23/40), you force a fractional division and a floating point number. The results from the first 2 calculations are not actually 57.5, they just appear that way. Before you close the books, look at this: > aa <- 100*(23/40) > bb <- (100*23)/40 > all.equal(aa,bb) [1] TRUE > round(aa) [1] 57 > round(bb) [1] 58 I'm putting this one in my collection of "difficult to understand" numerical calculations. If you have seen this before, I'm sorry to waste your time. pj -- Paul E. Johnson http://pj.freefaculty.org Director, Center for Research Methods and Data Analysis http://crmda.ku.edu To write to me directly, please address me at pauljohn at ku.edu. ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
