From: Jay Levitt <jay+news@...>
Date: 2007-09-26T14:20:08+09:00
Subject: Detecting number ranges

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