From: Rich Kilmer <rich@...>
Date: 2002-03-17T11:38:45+09:00
Subject: RE: sorting large string of records

How about this:

class StringView
  attr :offset

  def initialize(data, offset, len)
    @data = data
    @offset = offset
    @len = len
  end

  def <=>(other)
    @len.times do |i|
      case @data[@offset+i]<=>@data[other.offset+i]
      when -1
        return -1
      when 1
        return 1
      end
    end
    return 0
  end

  def to_s
    return @data[@offset, @len]
  end
end

# build your database and array
dbArray = []
database = "00080003000200060007000100040005"
len = 4
(database.length/len).times {|i| dbArray << StringView.new(database, i*len,
len)}

# sort and join
puts dbArray.sort.join


> -----Original Message-----
> From: Ron Jeffries [mailto:ronjeffries@REMOVEacm.org]
> Sent: Saturday, March 16, 2002 8:58 PM
> To: ruby-talk ML
> Subject: sorting large string of records
>
>
> Suppose I have a large string that is really a lot of fixed-size
> records joined
> together. And suppose that I don't really want to turn it into an array of
> strings.  (This last is a big supposition: I'm starting to think
> maybe I do want
> to. But go with me ...)
>
> I want to sort the records within the big string.
>
> Here's what I did because it was easy.
>
> 1. I have an object, StringView, that, given the string, an offset, and a
> length, can act like a single record from the big string. I was
> already using it
> to slice out fields from the "record".
>
> 2. I implemented <=> on StringView, by slicing the string that it
> views and
> sending <=> to that (and the string from the argument of course).
>
> 3. When the StringViews are sorted, I join('') them to get a new string
> assembled.
>
> This has the advantage of being easy but drawbacks include:
>
> 1. I have to slice the records out anyway
> 2. Slices occur more than N times, depending on the O() of Ruby's sort
> algorithm.
>
> Now if I were doing this in C or some language like that, I'd just use my
> StringView as a pointer, and look at the bytes of the string without
> instantiating a new object. A fairly simple loop over the characters could
> implement <=>.
>
> So ... is there a way to sort my big string without slicing it to smaller
> strings?
>
> Thanks!
>
> Ronald E Jeffries
> http://www.XProgramming.com
> http://www.objectmentor.com
> I'm giving the best advice I have. You get to decide whether it's
> true for you.
>