François Pinard wrote: > Hi, R people. > > In ?factor, in the "Examples:" section, we see: > > ## suppose you want "NA" as a level, and to allowing missing values. > (x <- factor(c(1, 2, "NA"), exclude = "")) > is.na(x)[2] <- TRUE > x # [1] 1 <NA> NA, <NA> used because NA is a level. > is.na(x) > # [1] FALSE TRUE FALSE > > I'm a bit confused by this example, as I do not understand the point > being made. Using 'exclude = ""' or not does not change the outcome. > What is being demonstrated by this clause, here? Isn't "NA" a mere > string, not really related to a missing value? > > It might also be some kind of linguistic problem, and I'm not a native > English speaker. The "and to allowing" construct sounds strange to me. > I would expect either "and to allow" or "and allowing", but maybe I'm > plainly missing the meaning of the statement. > > Could this be clarified somehow? > > I think this is a relic. In the olden days, there was no such thing as a missing character values, and factor() would behave like
> (x <- factor(c(1, 2, "NA"), exclude = "NA")) [1] 1 2 <NA> Levels: 1 2 ...which was a pain when dealing with abbreviations for "noradrenalin", "North America", "New Alliance", "Neil Armstrong", etc. So character NA was added to R, and the example became irrelevant without anyone noticing. ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
