From: Michael Glaesemann <grzm@...>
Date: 2007-08-03T10:31:00+09:00
Subject: Re: Determining the common prefix for several strings


On Aug 2, 2007, at 19:31 , Todd Burch wrote:

> I have several strings to analyze.  The strings are the names of a  
> list
> of things that were once ordered and now are not.  A typical array of
> names might look like this:
>
> item001
> item004
> item002
> item002b
> item002C
> item 5
> item 10
> itemize this
>
> I want to parse these names and determine that "item" is the common
> prefix.
>
> I know how to armstrong my way through it a character at a time,  
> but I'm
> thinking that Ruby probably has a very elegant way of doing this that
> I'm not familiar with yet.

I don't know of a particularly elegant way to do this in Ruby, but my  
initial thoughts are

list = <<-EOS
item001
item004
item002
item002b
item002C
item 5
item 10
itemize this
EOS
# sort by length: prefix can't be longer than shortest string.
items = list.split("\n").sort_by { |i| i.length }
# use shortest as prefix
first = items.shift
items.inject(first) do |prefix, item|
   next prefix if item.match(/^#{prefix}/)
   # have to go char by char
   n = 0
   for i in 0..(prefix.length - 1) do
     break if prefix[i] != item[i]
     n = i
   end
   prefix[0..n]
end

Michael Glaesemann
grzm seespotcode net