From: Florian Gross <flgr@...>
Date: 2004-12-14T06:07:19+09:00
Subject: Re: [Nuby] Sorting a Hash and keepint it as a Hash?

Williams, Chris wrote:

> I have a Hash of objects which I want to sort by the values. Afterwards
> I want to pull out the keys as one array and the values as another. So I
> have code like so:
> 
> # sort by frequency ascending
> @fault_sums = @fault_sums.sort {|a,b| a[1] <=> b[1]}
> # Only keep top N
> @fault_sums.slice!(0...-@number) if @number <= @fault_sums.size 
>     
> fields = @fault_sums.keys
> data = @fault_sums.values
> 
> But when I get to calling keys and values on the Hash I realized, sort
> actually returns back a 2D array and those methods aren't defined on an
> Array. Is there a way to make the 2D Array returned by the sort back
> into a Hash?

There's no sorted Hashs in Standard Ruby so you will get a sorted Array 
of pairs.

However you can use a nifty trick to get the keys and values out of that:

[['key1', 'value1'], ['key2', 'value2']].transpose
# => [['key1', 'key2'], ['value1', 'value2']]

So this will solve your problem:

top_pairs = @faults_sum.sort_by { |key, value| -value }.first(@number)
fields, data = *top_pairs.transpose

Note that I chose to sort descending and to keep the first (high sum) 
entries instead of sorting ascending and to keep the lowest (high sum) 
entries in reverse.