From: Robert Klemme <shortcutter@...>
Date: 2007-09-16T20:35:04+09:00
Subject: Re: Search for duplicate elements in the array

On 16.09.2007 13:04, Ruhe wrote:
> Hello.
> I have a pretty good working Java method, which sorts array of
> strings, then searches for duplicate elements. If element is
> duplicated output shows ">> hello *20 times" for example.
> 
> private void printArray()
> 
> 	{
> 
> 		String arr[] = str.split("\\n+");
> 
> 
> 
> 		Arrays.sort(arr);
> 
> 
> 
> 		for (int j = 0; j < arr.length; j++)
> 
> 		{
> 
> 			int count = 1;
> 
> 			for (int i = j + 1; i < arr.length; i++)
> 
> 			{
> 
> 				if (arr[i].compareTo(arr[j]) == 0)
> 
> 				{
> 
> 					count++;
> 
> 					j++;
> 
> 				}
> 
> 			}
> 
> 			if (count > 1)
> 
> 			{
> 
> 				System.out.println(">> " + arr[j] + " *" + count + " times");
> 
> 			} else
> 
> 			{
> 
> 				System.out.println(">> " + arr[j]);
> 
> 			}
> 
> 		}
> 
> 	}
> 
> 
> But the problem is that I can't write this method in Ruby! How to make
> this in Ruby?

This is way inefficient.  You rather want a counter per element stored 
in a Map (HashMap or TreeMap in Java).

dups = Hash.new 0
arr.each {|x| dups[x]+=1}
puts dups.select {|k,v| v>1}

You can have it on one line if you prefer:

puts arr.inject(Hash.new(0)) {|d,x| d[x]+=1; d}.select {|k,v| v>1}

Kind regards

	robert