[R] Consistant test for NAs in a factor when exclude = NULL?

[William Dunlap]

Note that for factors with NA in the levels, is.na(f)[2] <- TRUE
and is.na(f[2])<-TRUE give different results:

  > f <- factor(c("A","A",NA), levels=c(NA, "A"), exclude=NULL)
  > str(f)
   Factor w/ 2 levels NA,"A": 2 2 1
  > is.na(f)
  [1] FALSE FALSE FALSE

  > is.na(f[2]) <- TRUE
  > str(f)
   Factor w/ 2 levels NA,"A": 2 1 1
  > is.na(f)
  [1] FALSE FALSE FALSE

  > is.na(f)[2] <- TRUE
  > str(f)
   Factor w/ 2 levels NA,"A": 2 NA 1
  > is.na(f)
  [1] FALSE  TRUE FALSE

  > f[2] <- NA
  > str(f)
   Factor w/ 2 levels NA,"A": 2 1 1
  > is.na(f)
  [1] FALSE FALSE FALSE

You may find it easiest to change the NA's to strings
with a different name.

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com 

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of andrewH
> Sent: Wednesday, October 26, 2011 9:22 PM
> To: r-help at r-project.org
> Subject: Re: [R] Consistant test for NAs in a factor when exclude = NULL?
> 
> Thanks Jeff! I appreciate you sharing your experience.
> 
> My data set is survey data, 13,209 records over nine years, collected by
> someone else, converted from SPSS format. It includes missing values,
> identified however SPSS does so, and translated to NAs by the import
> process. It also includes values along the lines of "none of your business"
> or "beats me" that are missing so far as I am concerned. I have assigned NAs
> to these values.  Now I am trying to figure out some things about where
> these missing values are -- whether they are disproportionately located in
> any period or group.  I have been trying to get counts for subsets, but I
> have not been able to make the subset counts add up to the total counts that
> I get from, e.g. summary.
> 
> So I wrote these simplified versions, and even for the simplest examples, I
> could not find a function that correctly identified the NAs that I knew were
> there because I put them there myself. That is why I am looking for help.
> Does this make sense?
> 
> Warmest regards, andrewH
> 
> 
> --
> View this message in context: http://r.789695.n4.nabble.com/Consistant-test-for-NAs-in-a-factor-when-
> exclude-NULL-tp3942755p3943157.html
> Sent from the R help mailing list archive at Nabble.com.
> 
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