The help doc for readBin writeBin tells me this:
Handling R's missing and special (Inf, -Inf and NaN) values is discussed
in the ‘R Data Import/Export’ manual.
So I go here:
http://cran.r-project.org/doc/manuals/r-release/R-data.html#Special-values
Unfortunately, I don't really understand that. Suppose I am using
single-byte integers and I want 255 (binary 11111111) to be translated to
NA. Is it possible to do that? Of course I could always do something
like this:
X[ X==255 ] <- NA
The problem with that is that I want to process the data on the fly,
dividing the integer to produce a double in the range from 0 to 2:
X <- readBin( file, what="integer", n=N, size=1, signed=FALSE)/127
It looks like this still works:
X[ X==255/127 ] <- NA
It would be neater if there were some kind of translation option for the
input stream, like the way GNU tr (Linux/UNIX) works. I'm looking around
and not finding such a thing. I can use gsub() to translate on the fly
and then coerce back to integer format:
X <- as.integer(gsub("255", NA, readBin( file, what="integer", n=N, size=1,
signed=FALSE)))/127
What is your opinion of that tactic? Is there a better way? I don't know
if that has any advantage on the postprocessing tactic above. Maybe what
I need is something like gsub() that can operate on numeric values...
X <- numsub(255, NA, readBin( file, what="integer", n=N, size=1,
signed=FALSE))/127
...but if that isn't better in terms of speed or memory usage than
postprocessing like this...
X[ X==255/127 ] <- NA
...then I really don't need it (for this, but it would be good to know
about).
The na.strings = "NA" functionality of scan() is neat, but I guess that
doesn't work with the binary read system. I don't think I can scan the
readBin input because it isn't a file or stdin.
Mike
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