From: ara.t.howard@...
Date: 2006-03-30T00:40:00+09:00
Subject: Re: reading/writing binary problem

On Wed, 29 Mar 2006, Wolfgang wrote:

> Hi,
>
> I have some binary files which I need to delete some data at the beginning of 
> the file (to extract the raw data out of the file). I got a matlab file from 
> a colleque but I would prefer if I could do it with ruby.
>
> This matlab code does the trick:
> 	function m=write_rad(filename)
> 	file=fopen(filename);
> 	f= fread(file,'uint16');
>
> 	[r,k]=size(f);
> 	if k==1;
>   		t=r-1048576;
>   		m=f(t+1:r,:);
> 	end
> 	end % function
>
> How can I do this in ruby? I'm completely lost.
>
> Thanks
> Wolfgang

this sould be easy if i understood that method and the nature of your data ;-)

here's what i understand this method to do :

   # open the file

     file=fopen(filename);

   # read all available unit16 quantities into an [m, n] array

     f= fread(file,'uint16');

   # check the size of this array, r is the number of elements read

     [r,k]=size(f);

   # k will be one iff data was read into r dimension

     if k==1;

   # here i assume 1048576 is the 'row_size' of 1mb.  we set t to be the offset
   # of the last row

     t=r-1048576;

   # because matlab is evil and uses one based indexing, we inc t by one and
   # extract the last row/block of data.  but here it seems like the ith index
   # should be t+1:r-1048576 no?  otherwise it seems like this would be out of
   # bounds?

     m=f(t+1:r,:);


in any case this looks alot like you are trying to extract the last 1mb of
uint16 quantities from a data file - is that right?  let me know and i'll show
you how to do this.

regards.

-a
-- 
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