From: 7stud -- <bbxx789_05ss@...>
Date: 2011-04-28T03:31:17+09:00
Subject: Re: pattern matching and array methods

Mfer Dez wrote in post #995245:
> I have a text file that is structured like so:
>
> 1:1 abcdefg
> 1:2 abcdefg
> 1:3 abcdefg
> 1:4 abcdefg
> 1:5 abcdefg
>
> I would like to be able to print out a subset of the file ie: print the
> line beginning with 1:2 through the line beginning with 1:4
>

If do some work to save the lines in an easily accessible structure, you 
can make the lookup much easier:

lines = [

  '1:1 xxxxxx',
  '1:2 xxxxxx',
  '1:3 xxxxxx',
  '1:4 xxxxxx',
  '1:5 xxxxxx',
  '2:1 xxxxxx',
  '2:2 xxxxxx',
  '2:3 xxxxxx',
  '2:4 xxxxxx',
  '2:5 xxxxxx'
]


#Create a hash whose non-existent keys
#are automatically assigned an empty array:
h = Hash.new {|hash, key| hash[key] = []}

lines.each do |line|
  numbers, str = line.split(' ', 2)
  key, index = numbers.split(':')
  h[key][index.to_i] = line
  #If h[key] does not exist it will automatically
  #be assigned an empty array, which you can then
  #index into.
end

target = '2:2 - 2:5'
start, stop = target.split(/\s* - \s*/xms)
key1, index1 = start.split(':')
key2, index2 = stop.split(':')

index1, index2 = index1.to_i, index2.to_i
p h[key1][index1..index2]

--output:--
["2:2 xxxxxx", "2:3 xxxxxx", "2:4 xxxxxx", "2:5 xxxxxx"]

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