From: Xavier Noria <fxn@...>
Date: 2007-08-03T11:26:38+09:00
Subject: Re: Determining the common prefix for several strings

El Aug 3, 2007, a las 2:31 AM, Todd Burch escribi�:

> 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.

This is a solution that avoids going char by char:

   items = [
     'item001',
     'item004',
     'item002',
     'item002b',
     'item002C',
     'item 5',
     'item 10',
     'itemize this'
   ]

   min_length = items.map {|i| i.length}.min
   cuts = items.map {|i| i.split(//)[0, min_length]}
   cuts.transpose.each_with_index do |t, i|
     if t.uniq.length != 1
       puts cuts.first[0, i].join('')
       break
     end
   end

We first check which is the length of the shortest string in the  
array, then split by chars to store those many ones, and then  
transpose the matrix. Note that transposing is OK because we cut the  
strings. That's longer to explain than to write it in Ruby as you  
see. Once you get the transpose you can go row by row to detect the  
one that has more than one distinct element. Again that's easy  
delegating the job to uniq.

-- fxn