From: Raf Coremans <rrafje@...>
Date: 2007-09-28T05:33:10+09:00
Subject: Re: Detecting number ranges

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2007/9/26, Jay Levitt <jay+news@jay.fm>:
>
> I had to write a script this evening to take an unsorted input file of the
> form:
>
> database 1 is on server 3
> database 8 is on server 7
> ...
>
> and output it in the form:
>
> server 3 handles database 1 through 7
> server 7 handles database 8 through 11
>
> My brain was in procedural mode, and I wrote the following ugliness:
>
> ---
>
> def output_range(start_db, end_db, server_n)
>    puts "server #{server_n} handles database #{start_db} through
> #{end_db}"
> end
>
> open("db_list.txt").readlines.each do |line|
>   m = line.match(/^database (.*) is on server (.*)/)
>   db_n = m[1].to_i
>   server_n = m[2].to_i
>
>   db_servers[db_n] = server_n
> end
>
> range_start = 1
>
> db_servers.each_index do |i|
>    next if i == 1
>      if db_servers[i] != db_servers[i - 1]
>        output_range(range_start, i - 1, db_servers[i - 1])
>        range_start = i
>    end
> end
>
> last_db = db_servers.size - 1
> output_range(range_start, last_db, db_servers[last_db])
> ---
>
> which in fact is not only horrid to look at, but has a bug (it doesn't
> like
> it if the input skips over a database number, i.e. db 233 and 235 are
> present but 234 is missing).
>
> I feel like there's a much nicer way to express this in Ruby, but can't
> think of what it might be...
>
>
> --
> Jay Levitt                |
> Boston, MA                | My character doesn't like it when they
> Faster: jay at jay dot fm | cry or shout or hit.
> http://www.jay.fm         | - Kristoffer
>
>

Or use Set#divide:

require 'set'

ss = Set[*DATA.readlines.map{ |l| l.scan( /\d+/).map{ |s| s.to_i}.reverse}]

ss = ss.divide{ |i, j| i[0] == j[0] && (i[1] - j[1]).abs <= 1}

ss = ss.inject( {}){ |h, s| sa = s.to_a.sort; (h[sa.first[0]] ||= []) << (1
== sa.size ? sa.first[1] : sa.first[1]..sa.last[1]); h}

ss.keys.sort.each{ |k| puts "Server #{k} handles db #{ss[k].sort_by{ |d|
d.is_a?( Range) ? d.begin : d}.join( ', ')}"}

__END__
database 8 is on server 7
database 10 is on server 7
database 9 is on server 7
database 5 is on server 9
database 1 is on server 3
database 2 is on server 3
database 133 is on server 3
database 4 is on server 144


=>
Server 3 handles db 1..2, 133
Server 7 handles db 8..10
Server 9 handles db 5
Server 144 handles db 4



Regards,
R.

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