From: William James <w_a_x_man@...>
Date: 2007-01-25T01:05:07+09:00
Subject: Re: Text file parsing in ruby



On Jan 24, 9:33 am, Paul van Delst <Paul.vanDe...@noaa.gov> wrote:
> Hello,
>
> As I use ruby more and more for things, I find myself creating "Config" classes, filling
> them with data read from a simple text file, and then passing instances of config around
> to do all the work. What I would like to get some advice on, or links to, is ruby-ish
> methods of reading/parsing text files.
>
> A lot of text files have, for example, some sort of header that says how much data is
> coming, followed by the data itself, e.g.
>
> Number of data points: 5
> 1 2
> 3 4
> 5 6
> 7 8
> 9 0
> Number of data points: 2
> 10 20
> 11 21
> Number of data points: 20
> 1 2
> 2 3
> ..etc..
>
> Or, svn log output where the header line says how many lines of log message follow.
>
> I find I'm struggling to figure out a tidy way to read these sorts of files. If, for
> example, I iterate over the lines,
>
> IO.readlines(file_name).each do |line|
>    ...parse the line
> end
>
> How do I take advantage of the fact that the "header" line tells me how much actual data
> follows before the next header? I.e. I discover that I need to read 5 point so I read 5
> points and the next line that is parsed in the above iteration is the next header line.
> Sort of short-circuiting the iteration.
>
> The solution I've come up with so far is to use "sentinel" values that flag what is to
> come, but it's yuckily kludgy. Any tips from the 'sperts?
>
> Apologies if this is a CS101 type of question.
>
> cheers,
>
> paulv
>
> --
> Paul van Delst             Ride lots.
> CIMSS @ NOAA/NCEP/EMC               Eddy Merckx


open('data1'){|handle|
  while header = handle.gets do
    header[ /\d+/ ].to_i.times {
      p handle.gets
    }
  end
}