From: Tomasz Wegrzanowski <taw@...>
Date: 2002-01-06T10:50:37+09:00
Subject: [ruby-talk:30321] Re: Sorting a Hash by value of integer stored in the Hash

On Sun, Jan 06, 2002 at 10:34:57AM +0900, Michael Joner wrote:
> I have a program which creates a Hash array.  The ultimate result is a
> word as the key and an integer as the value.  I'd like to sort by the
> value in the Hash, then print the ten highest values and their associated
> keys.  I understand that there is a sort Method but I'm not sure how to
> get it to work on a Hash.  I know that if my data were simply stored in an
> array I could use:
> 
> myArray.sort { |a,b| b <=> a }
> 
> So I've tried the same technique on the Hash:
> 
> myHash.sort { |a,b| b <=> a }
> 
> Printing the first ten elements of the resulting object (which was an
> array) returned words starting with z and then y (in reverse alphabetical)
> and the associated value, run together.  This isn't what I'm trying to
> get.  The sort apparently was performed on the keys, but I want to do sort
> on the values.  Is there a way to do this?

If there aren't any duplicated elements, it's easiest to just invert the hash:

	hash_new = hash.invert
	...

and operate on inverted hash. If there are, it's probably easiest to
make hash of arrays:

	new_hash=Hash.new([])
	hash.each_pair { |k,v|
		new_hash[v].push k
	}
	...