[Rd] R 2.5.1 - ?factor examples, details

From: François Pinard <pinard_at_iro.umontreal.ca>
Date: Mon, 02 Jul 2007 22:18:06 -0400


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?

-- 
François Pinard   http://pinard.progiciels-bpi.ca

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