Hi Harold, Many (most?) of the statistics function have a similar argument. I suspect it is sort of to warn the user---you have to be explicit about it rather than the program just silently removing or ignoring values that would not work in the function called. I can think of one example where I want a missing value returned. In psychology we often create scores on some construct (say optimism), by averaging individuals' response to several questions. In certain cases if a subject does not respond to one question, their overall score should be missing. This is easily accomplished by letting na.rm = FALSE.
Cheers, Josh On Tue, Jul 12, 2011 at 9:26 AM, Doran, Harold <hdo...@air.org> 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? > > 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 > > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org mailing list > 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. > -- Joshua Wiley Ph.D. Student, Health Psychology University of California, Los Angeles https://joshuawiley.com/ ______________________________________________ R-help@r-project.org mailing list 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.
