R help - May 2010 - handling nulls while reading mainframe file

Hi,

I am trying to read in records from an old main frame file. Each record is
640 bytes. I had some success using the following statement:

iconv(readChar(con, nchars=640, useBytes
TRUE),from="IBM037",to="",sub="#")

What I have found, however, is that ocassionally a record will contain a
Null halfway through, which causes readChar() not to read the rest of the
record. It is a very old database (from the 1970s I think), and I am not
really sure why the Nulls are there. I do know that that after the occurence
of the first Null, the record looks normal (it's not Nulls to the 640th
byte). In any case, I would like to get the whole record and just put some
placeholder, like a 0 or a #, in place of the Nulls.

I tried using readBin() instead, but I couldn't figure out how to pass that
off to iconv...

Can anyone help?

Thanks,
Mike

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Try using readBin and 'raw'

x <- readBin('yourFile', 'raw', n=1e6)

You can then scan 'x' and replace NULLs (I assume they are 0x00) with
whatever you want.
> str(x)
 raw [1:10] 00 00 22 00 ...
> x
 [1] 00 00 22 00 00 00 00 00 00 00
> x[x == as.raw(0)] <- as.raw(0xab)
> x
 [1] ab ab 22 ab ab ab ab ab ab ab
>

On Wed, May 5, 2010 at 1:07 PM, Michael Steven Rooney <
michael.s.rooney@gmail.com> wrote:
> Hi,
>
> I am trying to read in records from an old main frame file. Each record is
> 640 bytes. I had some success using the following statement:
>
> iconv(readChar(con, nchars=640, useBytes >
TRUE),from="IBM037",to="",sub="#")
>
> What I have found, however, is that ocassionally a record will contain a
> Null halfway through, which causes readChar() not to read the rest of the
> record. It is a very old database (from the 1970s I think), and I am not
> really sure why the Nulls are there. I do know that that after the
> occurence
> of the first Null, the record looks normal (it's not Nulls to the 640th
> byte). In any case, I would like to get the whole record and just put some
> placeholder, like a 0 or a #, in place of the Nulls.
>
> I tried using readBin() instead, but I couldn't figure out how to pass
that
> off to iconv...
>
> Can anyone help?
>
> Thanks,
> Mike
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
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> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
>
http://www.R-project.org/posting-guide.html<http://www.r-project.org/posting-guide.html>
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?

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