R help - Feb 2001 - Reading single precision floats from binary file

Dear all,

I have a few files with binary data written by a C program a friend wrote.
I allready have program to read these files, Thomas Lumley and Prof Brian
D Ripley was kind enough to respond to a question to this list earlier
with some code that works perfectly, so this is really no problem, it is
more out curiousity.

Most of my files consists of 40000 single precision floats, and I figured
the new readBin() function exists for the purpose of reading such files,
so I tried to use it, but with no success.

Now, the docs say that what you can read is "numeric",
"double",
"integer", "int", "logical", "complex",
"character", and since "single" is
not on the list, is it simply not the right tool for the job?
I tried different things, among them, providing single as what,
changing the size, etc, but it always ends up with reading 20000 records,
indicating that it does read the file as double precision floats.

It is not clear to me what the last sentence in the notes for this
function means, and indeed not quite clear what the function does at all,
but I was hoping someone can enlighten me.

Best,

Kjetil
-- 
Kjetil Kjernsmo
Graduate astronomy-student                    Problems worthy of attack
University of Oslo, Norway            Prove their worth by hitting back
E-mail: kjetikj at astro.uio.no                                - Piet Hein
Homepage <URL:http://www.astro.uio.no/~kjetikj/>
Webmaster at skepsis.no




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Kjetil Kjernsmo <kjetil.kjernsmo at astro.uio.no> writes:
> Dear all,
> 
> I have a few files with binary data written by a C program a friend wrote.
> I allready have program to read these files, Thomas Lumley and Prof Brian
> D Ripley was kind enough to respond to a question to this list earlier
> with some code that works perfectly, so this is really no problem, it is
> more out curiousity.
> 
> Most of my files consists of 40000 single precision floats, and I figured
> the new readBin() function exists for the purpose of reading such files,
> so I tried to use it, but with no success.
> 
> Now, the docs say that what you can read is "numeric",
"double",
> "integer", "int", "logical",
"complex", "character", and since "single" is
> not on the list, is it simply not the right tool for the job?
> I tried different things, among them, providing single as what,
> changing the size, etc, but it always ends up with reading 20000 records,
> indicating that it does read the file as double precision floats.
> 
> It is not clear to me what the last sentence in the notes for this
> function means, and indeed not quite clear what the function does at all,
> but I was hoping someone can enlighten me.

Works OK for me with the current patch version, except that the nparameter to
readBin seems to be misdocumented:

x<-rnorm(100)
zz <- file("testbin", "wb")
writeBin(x, zz, size=4)
close(zz)
system("ls -l testbin")

zz <- file("testbin", "rb")
xx <- readBin(zz, numeric(), n= 999999, size=4)
length(xx)
range(x - xx)
close(zz)

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
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> Date: Thu, 15 Feb 2001 17:04:48 +0100 (MET)
> From: Kjetil Kjernsmo <kjetil.kjernsmo at astro.uio.no>
> To: R Help list <r-help at stat.math.ethz.ch>
> Subject: [R] Reading single precision floats from binary file
> 
> Dear all,
> 
> I have a few files with binary data written by a C program a friend wrote.
> I allready have program to read these files, Thomas Lumley and Prof Brian
> D Ripley was kind enough to respond to a question to this list earlier
> with some code that works perfectly, so this is really no problem, it is
> more out curiousity.
> 
> Most of my files consists of 40000 single precision floats, and I figured
> the new readBin() function exists for the purpose of reading such files,
> so I tried to use it, but with no success.
> 
> Now, the docs say that what you can read is "numeric",
"double",
> "integer", "int", "logical",
"complex", "character", and since "single" is
> not on the list, is it simply not the right tool for the job?
R does not have a "single" mode for vectors, and that is what it says
you can
specify as `what'.
> I tried different things, among them, providing single as what,
> changing the size, etc, but it always ends up with reading 20000 records,
> indicating that it does read the file as double precision floats.
> 
> It is not clear to me what the last sentence in the notes for this
> function means, and indeed not quite clear what the function does at all,
> but I was hoping someone can enlighten me.
It is indeed what readBin is for, and for me

readBin(con, "double", n=40000, size=4)

works.  Indeed, there are examples of this in the help page for readBin.

Test:

zz <- file("testbin", "wb")
writeBin(rnorm(20000), zz, size=4)
close(zz)
system("ls -l testbin") # 80000
zz <- file("testbin", "rb")
a <- readBin(zz, numeric(), n = 20000, size=4)
length(a) # 20000
close(zz)


-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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