From ben@eno.princeton.edu  Tue May 11 14:33:37 1999
From: ben@eno.princeton.edu (Ben Bolker)
Date: Tue, 11 May 1999 09:33:37 -0400 (EDT)
Subject: matrix() can't handle NaN (PR#193)
In-Reply-To: <Pine.LNX.3.96.990511141530.8636A-100000@cbe207.gcal.ac.uk>
Message-ID: <Pine.SUN.3.91.990511092658.11064E-100000@paca>

On Tue, 11 May 1999, Bill Simpson wrote:


 [examples with read.table(...,na.strings="NaN") snipped]
> 
> >   "NaN" (Not a Number) as seen in debuggers, etc., is not the same as "NA"
> > as a "not available/applicable" value in R.
> 
> Yes, I realize that.
> However, since there is an R function is.nan(), and through experiments at
> the command line like this
> > xx<-NaN
> > xx+1
> NaN
> I thought that NaN was recognized by the R system and obeyed the proper
> rules. Same for Inf and -Inf.
> 
> Or are these things only sometimes recognized and sometimes not? Shouldn't
> they be employed consistently?
> 
> Bill
> 

  I'm going to defer this to people who know more than I about 
consistency and the differences between NA and NaN.  I will note that
the help for is.na() says:

The generic function `is.na' returns a logical vector of the same ``form''
as its argument `x', containing `TRUE' for those elements marked `NA' or
`NaN' (!) and `FALSE' otherwise.

  The (!) suggests that whoever wrote the help file recognized some 
subtlety here ... [similarly, is.finite() recognizes NA as a non-finite 
number]

  This seems to fall in the general category of "how do we help people 
avoid 'gotchas' in R that, while logical, are not necessarily what they 
expect?  Can we do this without blurring logical distinctions that are 
interesting/important/significant to more knowledgeable users?"

  One *could* extend the default na.strings in read.table to 
c("NA","NaN"), which would take care of the immediate problem but might 
further blur the subtle distinction between NA and NaN.  I don't know 
how/whether one would want to extend read.table() to deal with Inf/-Inf 
in data files ... (I think not).

  Ben
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matrix() can't handle NaN (PR#193)
Ben Bolker